Civil Engineering: January 2012

Monday, January 2, 2012

Things to remember during Concrete Mix Design

Good quality concrete starts with the quality of materials, cost effective designs is actually a by-product of selecting the best quality material and good construction practices. Following are 10 Things to remember during Concrete Mix Design and Concrete Trials.
1. ACI and other standards only serves as a guide, initial designs must be confirmed by laboratory trial and plant trial, adjustments on the design shall be done during trial mixes. Initial design “on paper” is never the final design.

2. Always carry out trial mixes using the materials for actual use.

3. Carry out 2 or 3 design variations for every design target.

4. Consider always the factor of safety, (1.125, 1.2, 1.25, 1.3 X target strength)

5. Before proceeding to plant trials, always confirm the source of materials to be the same as the one used in the laboratory trials.

6. Check calibration of batching plant.

7. Carry out full tests of fresh concrete at the batching plant, specially the air content and yield which is very important in commercial batching plants.

8. Correct quality control procedures at the plant will prevent future concrete problems.

9. Follow admixture recommendations from your supplier (of course Sika)

10. Check and verify strength development, most critical stage is the 3 and 7 days strength.

Important note:

Technical knowledge is an advantage for batching plant staff, even if you have good concrete design but uncommon or wrong procedures are practiced it will eventually result to failures.

RCC Mix Design

Mix design proportioning methods for Roller Compacted Concrete RCC:

ACI 207.5R (chapter 2.4) and ACI 211.3R extensively described the mix design proportioning methods for no slump concrete applicable for Roller Compacted Concrete RCC

Materials Used in RCC mix design
a) Cementitious materials:
Cement content is generally low (typically 70 to 130 kg/m3). Any kind of Portland Cement (but low heat cement is a preferred type when its is available)

Fly Ash: Class F pozzolans are preferred. When used pozzolans, may replace up to 80 % of cement content.

b) Aggregates:
Selection of aggregates and control of aggregates quality is essential. Aggregates shall meet ASTM C33 standard.

Coarse aggregates:
Most of project use a coarse aggregates with a Nominal Maximal Size Aggregate (NMSA) between 37.5 and 75mm. The thickness of placement layer shall be more than 3 times the NMSA.

Fine aggregates:
The grading of fine aggregates strongly influence paste requirements and compactibility of RCC. It also affects water and cementitious material requirements needed to fill the aggregates voids and coat aggregate particles.

Other aggregates: Fines (crusher fines…):
In low cement content mixtures, supplements fines (material passing 0.075 mm sieve) are usually required. Fines quantities is generally 5% of total aggregates

c) Admixtures:
Admixtures for RCC needed mostly for set retardation (and plasticizing) effect. Water Reducer Type D (WR + retarder)
WR use is beneficial for strength gain, and retardation which can be required very extended. Main Sika Product for RCC: Plastiment TM 25 specifically designed for RCC.

Mix design considerations:
a) Workability / Consistency:
Measured with a Vebe vibrating table (ASTM C 1170).
The test principle is to measure the time for the concrete to be consolidated by vibrating in a cylindrically shaped mold. The longer the time, the drier/lesser workable is the concrete. Vebe times of RCC mixtures is generally from 10 to 40 seconds. Comparison of concrete consistency measured by slump and Vebe apparatus. ACI 211.3R

Consistency Slump (mm) Vebe (s)
Extremely dry - 32 to 18
Very Stiff - 18 to 10
Stiff 0 to 25 10 to 5
Stiff Plastic 25 to 75 5 to 3
Plastic 75 to 125 3 to 0
Very plastic 125 to 190 -

b) Strength:
Design strength of RCC dam is often based on long term strength (90 days, 120 days or even 1 year!). The strength of RCC is a function of w/c ratio only for mixture with Vebe time of ~ 15 to 20 sec. range. For drier mix, the strength is more controlled by the moisture-density relationship.

If water content is less than optimum => voids in structure, poorly compacted concrete with loss in density and strengths.

Compressive strength of RCC is usually measured by testing cylinder (15cm diameter, 30cm long).

Strength measured on cores is also possible.

d) Segregation:
It is necessary to produce mixture with minimum tendency to segregate => Aggregates (especially with NSMA > 37.5mm) shall be well graded.

Higher cement content mixture are generally more cohesive => less tendency to segregate.

e) Permeability
Mixture with paste volume of 18 to 22% by mass shall provide suitable level of impermeability. Higher cementitious content or high workability mixes that bond well to fresh lift joints will produce watertightness.

For lower cementitious content mix, and/or low workability mix, a bedding mortar between lifts may be needed.

f) Heat Generation:
It is an important factor considering the massive structures. Limitation of cement content, and/or use of fly ash is helping reduce heat generation.

g) Durability:
RCC should be free of damaging effects of alkali-aggregate reactivity

Quality control of RCC concrete:
Vebe Consistency Test
Density and air voids tests.
Moisture/water content tests.
Cement content evaluation
Temperature monitoring
Test (cylinders) specimens:
- Using modified Vebe apparatus (generally for mix with Vebe up to 20 seconds),

- Using of special vibrating hammers

Beware, because of low early strength of concrete specimens are “fragile”.

Lift-Joint sealing systems:
Lift joints shall be kept moist before placing next lift and normally do not require special treatment. In some cases, it is required to apply a “flowable” bedding mortar which need to be retarded with admixtures.

Concrete Mix Design Secrets

In order to make a concrete mix design that works, you should master all the concrete theories in combination with experiences of concreting at work. Here is some important things you need to know when design concrete mixes.

A. What do you need to know before designing concrete?
1. What are the strength requirements?

- Compressive (on cube or cylinder specimen) strength

- Flexural strength

- Tensile strength

2. What is the placing method? By pump or direct pouring?

3. How far is the job site from the batching plant?

4. What is the structure for casting? Pavement, foundation, elevated slab, etc.

5. What are the projects specification?

- Maximum or minimum cement contents

- Maximum water/cement ratio

- Slump or consistency limit

- Minimum Strength requirement @28 days

- Material specifications (what is the maximum size of aggregate?)

6. Latest testing results of materials is needed in the preliminary selection of materials and design calculation

B. What are Design Precautions and Things to Remember when design concrete mixes?
1. Increasing the sand/total aggregate ratio, increases the water requirement at the same consistency.

2. Increasing the water/cement ratio decreases the strength of concrete at the same cement content.

3. Remember that adding 5 liters of water per cubic meter increases the slump by 2.5cm.

4. Remember that adding 5 liters of water per cubic meter decreases strength by approximately 4%.

5. Always follow recommended admixture dosage.

6. Always have “control” when performing trial mixes, always perform trial mixes with another mix using the same materials. This data can be useful in diagnostics if a problem occurs.

7. Always adjust batching quantities to the actual moisture condition of the aggregates.

8. Volume tolerance for 1m3 concrete is 1 ± 0.2m3.

9. Range of normal weight concrete is from 2,200 kg/m3 to 2,400 kg/m3

9 Questions Before Making Shotcrete Mix Design

Before making a mix design for shotcrete or sprayed concrete, it is needed to get sufficient information from the clients. Adequate support information will be resulted in technically and economically effect for the work. A proper mix design assure a successful trial and thus, successful application on site.

Hereafter is a list of 9 questions to the ask the clients prior to making a shocrete mix design:

1. The location of shotcrete to be applied? Slope stabilization, overhead and wall in tunnel
2. Wet or Dry process will be applied? Normally, dry process for slope stabilization, wet process for tunnel lining.
3. The requirement of early strength (8 hours, 72 hours, 7 days, 28 days) and the final strength at each location.
4. Slump requirement (for wet process only)
5. What accelerator admixture to be used? Please note that it would be better to use liquid admixture in rainy season.
6. What is the concrete spraying machine to be used? Rotor Machine (for both wet and dry process) or Pump Machine (wet process only)
7. What kind and type of cement to be used (cement should be super fine. Blain Surface fineness is greater than 4000 square centimeter per gram) PC cement is most suitable for early strength requirement.
8. A dispenser system need to be installed in case wet process is used. Is such liquid dosing unit available?
9. Any other information is helpful in designing shotcrete mix?

Once these question get answered, the mix designing process can be started. For shotcrete or sprayed concrete, trial is a must be prior to the issue of mix design for actual application.

What is shotcrete?

Shotcrete or gunite was invented by Mr. Carl Ethan Akeley (1864-1926) in 1910. For attractions of a park, this American Architect was mandated to realize in concrete the reproduction of a dinosaur. Considering the sizes of the structure, he had the idea to develop a “cement gun” machine allowing the spraying of a cementitious mortar. Shotcrete was created!

Probably a symbolic coincidence, but the same year, Mr. Kaspar Winkler founded Sika. Since that time Sika has greatly contributed to the development of the shotcrete technology. By shotcrete technology development, we mean the continuous development of chemical additives and admixtures for shotcrete and as well the development of spraying equipments.

Fields of shotcrete application
Shotcrete is mainly used in Underground construction projects as preliminary or permanent structural support. By Underground constructions, we mean the construction of structures like road-rail tunnel, hydropower plant, mines, parking, subway, metro, storage area etc.
However shotcrete is as well as an economical tool to realize stabilization work (slope), swimming pools, waterways, concrete repairs, inner lining and architectural structures. About 90% of the shotcrete applied goes into Underground construction projects. Total volume of shotcrete worldwide applied yearly is more than 12 millions cubic meters

What is shotcrete?
As per the American Concrete Institute (ACI), shotcrete can be defined as a mortar or concrete, pneumatically projected at high velocity through a pressure resistant conveying line onto a surface, where it is compacted on impact.

Cement, sand, aggregate, water, additives and admixtures are the components entering in the production of the shotcrete mix.

Compared to normal concrete, shotcrete differs mainly from three points:

The maximal size of the aggregate used.
The way to place it.
The mixture of shotcrete can be dry or wet.
Regarding terminology we can describe Gunite as sprayed mortar while Shotcrete as a sprayed concrete.
By gunite we means a cementitious mixture of which the particles size is limited to 8 mm.
For shotcrete we consider the use of aggregates of which the maximal size is 16 mm. However, in the last 10 years there is a tendency to limit the maximal aggregate size to 12 mm.

Shotcrete development can be summarized from its start to nowadays as follows:
Dry process –> dry process with powder accelerator –> wet process with Alkali liquid accelerator –> wet process with Alkali free accelerator.

Shotcrete mix design and proportion

Aggregate

Aggregates for shotcrete my contain river sand, crushed sand and crushed stone with particle sizes up to 16mm, normally up to 9.5mm.

Here after is a typical and recommended gradation of combined aggregates for shotcrete that will resulted in perfect mix design.:

Water Cement Ratio

The water-cement ratio for wet shotcrete normally falls within a range of by weight and 0.40 to 0.55 for wet-mix shotcrete.

Dry mix design shall only include water content enough for the hydration process of cement needed for strength development.

In dry-mix shotcrete, the moisture content of the fine and coarse aggregates should be such that the aggregate-cement mixture will flow at a uniform rate, without slugging or hose plugging. The optimum moisture content is generally within the range of 3 to 6 percent. The sand should be dried or wetted as required to bring the moisture content within that range. Large fluctuations in moisture content should be avoided.

A crude but effective test for determining proper predampening is the “ball-in-hand” test. A small amount of mix is placed in the hand and squeezed tightly. When the hand is opened, the mixture may crumble into discrete particles which indicates too little predampening moisture and is usually light gray. If the material holds together, or cracks but remains essentially whole, there is enough moisture. If moisture comes off on the hand, there is too much moisture in the mix.

Unit Weight of Concrete

The unit weight of good shotcrete is usually between 2230 to 2390 kg/m3, about the same as conventional concrete.

Cement Content

OPC cement with surface Blaine above 4500 cm2/gr is most suitable for shotcrete. Typical and recommended cement contents is:

* It is in the best interest of the end user to perform trial mixes and shotcrete trial to determine the suitable cement content, to meet other parameters, above table is used only as a guide in preliminary design and shall be decided in the results of trial mixes and trial application.

Proportioning

Shotcrete design for wet process can be designed like conventional concrete but these mixes contains higher volume of fine aggregate and cement. Shotcrete process can be designed by absolute volume method or by weight.

Shotcrete design for dry process is designed using the bulk densities of the materials, usually the water content is not included in the calculation.

Application of sprayed concrete or shotcrete

Uses of sprayed concrete (or shotcrete)
Over the past century, sprayed concrete has replaced the traditional methods of lining tunnel profiles and has become very important in stabilizing the excavated tunnel section. Sprayed concrete is a single term that describes various component of a complete technology:

the material sprayed concrete
the sprayed concreting process
the sprayed concrete system
Sprayed concrete construction is used in many different types of project. The flexibility and economy comes to the fore in above-ground and underground buildings, tunneling and special underground construction, in fact throughout the construction industry. The following uses are widespread:

excavation stabilization in tunnelling and underground construction
tunnel and underground chamber lining
stabilization in mine and gallery construction
concrete repair (concrete replacement and strengthening)
restoration of historic buildings (stone structure)
sealing works
trenching stabilization
slope stabilization
protective lining
wearing courses
special lightweight load-bearing structures
creative applications
In terms of importance, tunnelling, mining and concrete repair head the list. In tunneling and mining, the main uses are for excavation stabilization, temporary and permanent arch lining. Sprayed concrete is also used fir all other appropriate concrete works. Large cavities are often spray filled, for instance. Spray concrete has confirmed and strengthen its position alongside tunnel segment lining (tubbing) and interior ring concrete as the main concreting method. The limits on its use lie in the technical and economic interfaces with the other concreting process and/or construction methods.

Types of construction using sprayed concrete (shotcrete)
Sprayed concrete is used in all areas of tunneling construction – for road or rail tunnels, water drainage and underground military structures, in addition to slope stabilization. Whether tunneling under a building or driving through an obstruction, the construction method is determined by the weight-bearing properties and stability of the substrate tunneled through. The main distinction is between full excavation of the entire section in one operation and partial excavation in many different forms and methods. If full excavation is not possible due to the rock stability, the final profile is often excavated is several phases.

In underground construction, because high stresses would often be exerted on the newly places excavation stabilization and lining. Predetermined deformation of the excavated section is often allowed and only then is the stabilization given a non-positive seal. This causes the stress to be distributed around the excavation section and in the area around the excavation face.

Keep reading next coming post: Sprayed concrete for stabilization and lining.

Fibre Reinforced Concrete

Conventional concrete containing discontinuous discrete fibres is called fibre-reinforced concrete. Fibers of various shape and size produced from steel, plastic, glass, carbon and natural materials have been used.
However for any reinforcement to be effective, it must be stiffer than the concrete matrix that is reinforcing. Generally the less stiff fibres (made from plastic and natural materials) only offer benefits in improving the tensile strength of plastic and semi-hardened concrete and are therefore mainly used to reduce plastic shrinkage and plastic settlement cracking. The stiffer fibres improve both the tensile strength and the toughness of harden concrete.

The most widely used stiff fibre is steel. Low volume fractions of fibres (less than 1%) are used to reduce shrinkage cracking. Moderate volume fractions (between 1% to 2%) increase flexural strength, fracture toughness and impact resistance. High volume fractions (greater than 2%) lead to strain hardening of the composites. The shape and length of the fibres also play a role in the fibres’ effectiveness in improving the properties of the concrete. The use of fibres in concrete can have a marked effect on the workability of the concrete and this need to be taken into account in the mix proportion of fibre-reinforced concrete.

Currently a great deal of research is being undertaken into the use of ultra-high-performance fibre-reinforced composites. One of the benefits of these materials is extremely high ductility. Fibre-reinforced concrete has been used for precast panels, airfield and highway pavements, industrial floors and in spraying concrete for slope stability and underground mining applications.

Concrete Countertops for your Home

The biggest reason you could have to choose concrete countertops over any other kind would be to take advantage of the inexpensive nature of the material. Nothing could be simpler and more readily available than poured concrete. Of course, no one likes the drab gray of plain concrete. Anyone who wants something more colorful can easily use staining – a method that is both cheap and simple.

The great thing about deciding to use a concrete for a countertop is that the material does lend itself well to DIY projects – even by novices who have little experience with it. Any investment you put into concrete is repaid well too – there’s quite nothing like concrete even among materials that last. Even used in places where it is exposed to the elements, concrete tends to last for at least a half-century once properly laid.

So concrete is cheap, durable and easy to work with. Isn’t there anything that works against it as a material of choice to use on countertops? Well, you could consider the cost of the sealing material that you need to use on top of laid concrete that would actually make it suitable for use as a countertop. Since countertops need to be buttery smooth in a way concrete just isn’t, you really need to consider finishing a countertop after you’ve laid it. The sealer makes the surface smooth enough and stain-proofed enough, for everyday use. If you don’t feel that you’re up to the task of building a concrete countertop yourself, having a professional come in and do it for you can turn out to be a somewhat expensive service to buy too.

If you do take the plunge and decide to get your feet wet, learning how to put down a concrete slab yourself, if you aren’t careful, you might find yourself in in a little too deep. Wrongly done, concrete can cure unevenly and developed cracks. And concrete countertops, even if you do succeed in installing them properly, do present quite a challenge when you need to to install a sink or something. The material is one of the hardest known to man, and cutting an even opening without damaging everything can be a serious problem. You also need to consider how concrete ages. While the structural integrity of the material can be untouchable for centuries, the glossy sealer overlay can have a finite life.

Concrete happens to be a material that’s easy to achieve mediocre results with, and difficult to finish with perfection. If you can afford to call in a professional, or if you can afford to take the time to learn really well how it is done in the DIY method, it could be the right material for your home.

Specification for Placing of Concrete

Concrete shall be deposited as nearly as possible to its final position and shall be placed in layers not more than 30 cm thick. Concrete shall be placed at such a rate that it is at all times plastic and will flow readily around reinforcement and embedded parts. Once placing is started, it shall be a continuous operation until the lift is completed. The area of placement shall not be more than that which can be completed in one pour in compliance with this specification.

The time between placing of successive layers forming a lift shall be short enough to permit a vibrator to penetrate the lower layer while the upper layer is being compacted. The minimum time between completion of a lift and the commencement of placing of a succeeding lift shall be 72 hours.

Pneumatic placing and pumping of concrete may only be used with the approval of client. In such a case, discharge lines shall be horizontal or inclined upwards. The discharge end shall not be more than 3m from the point of placement and shall supply a continuous stream of concrete without air pockets. Aluminum piping shall not be used.

During hot weather, special precautions, as directed or approved by the owner, shall be taken to ensure that the temperature of the concrete when it is placed does not exceed 30 degrees Centigrade. These may include, but shall not be limited to, the use of chilled mixing water, cooling of aggregate or working at night.

Concrete shall not be placed in exposed areas during rain and, should it rain while placing is in progress, the placed concrete shall be covered with vinyl or other impervious sheets. Placing may be resumed only when rain stops well before initial set of the placed concrete occurs. Otherwise, placing operations shall cease and the boundaries of the pour shall be prepared as specified for construction joints.

Concrete shall not be placed under water except when specifically directed and authorized in writing by the owner. In such a case, placing shall be done from a bottom?discharging watertight bucket or by termite pipe penetrating the previously placed concrete so that fresh concrete is always deposited below the surface and the operation is continuous until completion of the pour.

Compaction

Concrete shall be compacted by mechanical vibrators electrically or pneumatically driven. Immersion vibrators shall operate, when fully immersed, at speeds of not less than 7,000 impulses per minute for vibrating heads of less than 10 cm diameter and 6,000 impulses per minute for heads 10 cm or greater in diameter. They shall be slowly immersed and withdrawn vertically at spacing of 30 cm to 50 cm, with vibration periods of 10 to 15 seconds for each penetration, and shall penetrate into the layer below. Vibrators shall not come into contact with reinforcement or embedded parts.

Where immersion vibrators cannot be used, the concrete shall be compacted by form vibrators, rigidly attached to the outside of the form, operating at not less than 8,000 impulses per minute.

Curing

Concrete surfaces shall be kept continuously moist for at least 14 days after placing and until the concrete temperature produced by heat of hydration of the cement has peaked and fallen at least 10 centigrade degrees. Initial curing of exposed surfaces shall be performed by atomized water spray positioned so that all surfaces to be cured are constantly moist, or by a continuous layer of burlap kept constantly wet. Hand sprinkling shall not be used except in conjunction with the burlap alternative.

Forms capable of moisture loss, such as plywood forms, shall be regularly sprinkled with water to avoid loss of moisture from formed surfaces of the concrete.

Sunday, January 1, 2012

Self-healing Electronics Could Work Longer and Reduce Waste

When one tiny circuit within an integrated chip cracks or fails, the whole chip -- or even the whole device -- is a loss. But what if it could fix itself, and fix itself so fast that the user never knew there was a problem? A team of University of Illinois engineers has developed a self-healing system that restores electrical conductivity to a cracked circuit in less time than it takes to blink. Led by aerospace engineering professor Scott White and materials science and engineering professor Nancy Sottos, the researchers published their results in the journal Advanced Materials.

"It simplifies the system," said chemistry professor Jeffrey Moore, a co-author of the paper. "Rather than having to build in redundancies or to build in a sensory diagnostics system, this material is designed to take care of the problem itself."

As electronic devices are evolving to perform more sophisticated tasks, manufacturers are packing as much density onto a chip as possible. However, such density compounds reliability problems, such as failure stemming from fluctuating temperature cycles as the device operates or fatigue. A failure at any point in the circuit can shut down the whole device.

"In general there's not much avenue for manual repair," Sottos said. "Sometimes you just can't get to the inside. In a multilayer integrated circuit, there's no opening it up. Normally you just replace the whole chip. It's true for a battery too. You can't pull a battery apart and try to find the source of the failure."

Most consumer devices are meant to be replaced with some frequency, adding to electronic waste issues, but in many important applications -- such as instruments or vehicles for space or military functions -- electrical failures cannot be replaced or repaired.

UCLA Neuroscientists Demonstrate Crucial Advances İn 'Brain Reading'

At UCLA's Laboratory of Integrative Neuroimaging Technology, researchers use functional MRI brain scans to observe brain signal changes that take place during mental activity. They then employ computerized machine learning (ML) methods to study these patterns and identify the cognitive state -- or sometimes the thought process -- of human subjects. The technique is called "brain reading" or "brain decoding." In a new study, the UCLA research team describes several crucial advances in this field, using fMRI and machine learning methods to perform "brain reading" on smokers experiencing nicotine cravings.

The research, presented last week at the Neural Information Processing Systems' Machine Learning and Interpretation in Neuroimaging workshop in Spain, was funded by the National Institute on Drug Abuse, which is interested in using these method to help people control drug cravings.

In this study on addiction and cravings, the team classified data taken from cigarette smokers who were scanned while watching videos meant to induce nicotine cravings. The aim was to understand in detail which regions of the brain and which neural networks are responsible for resisting nicotine addiction specifically, and cravings in general, said Dr. Ariana Anderson, a postdoctoral fellow in the Integrative Neuroimaging Technology lab and the study's lead author.

"We are interested in exploring the relationships between structure and function in the human brain, particularly as related to higher-level cognition, such as mental imagery," Anderson said. "The lab is engaged in the active exploration of modern data-analysis approaches, such as machine learning, with special attention to methods that reveal systems-level neural organization."

For the study, smokers sometimes watched videos meant to induce cravings, sometimes watched "neutral" videos and at sometimes watched no video at all. They were instructed to attempt to fight nicotine cravings when they arose.

New Technique Makes İt Easier To Etch Semiconductors

Creating semiconductor structures for high-end optoelectronic devices just got easier, thanks to University of Illinois researchers. The team developed a method to chemically etch patterned arrays in the semiconductor gallium arsenide, used in solar cells, lasers, light emitting diodes (LEDs), field effect transistors (FETs), capacitors and sensors. Led by electrical and computer engineering professor Xiuling Li, the researchers describe their technique in the journal Nano Letters.

A semiconductor's physical properties can vary depending on its structure, so semiconductor wafers are etched into structures that tune their electrical and optical properties and connectivity before they are assembled into chips.

Semiconductors are commonly etched with two techniques: "Wet" etching uses a chemical solution to erode the semiconductor in all directions, while "dry" etching uses a directed beam of ions to bombard the surface, carving out a directed pattern. Such patterns are required for high-aspect-ratio nanostructures, or tiny shapes that have a large ratio of height to width. High-aspect-ratio structures are essential to many high-end optoelectronic device applications.

While silicon is the most ubiquitous material in semiconductor devices, materials in the III-V (pronounced three-five) group are more efficient in optoelectronic applications, such as solar cells or lasers.

Unfortunately, these materials can be difficult to dry etch, as the high-energy ion blasts damage the semiconductor's surface. III-V semiconductors are especially susceptible to damage.

To address this problem, Li and her group turned to metal-assisted chemical etching (MacEtch), a wet-etching approach they had previously developed for silicon. Unlike other wet methods, MacEtch works in one direction, from the top down. It is faster and less expensive than many dry etch techniques, according to Li. Her group revisited the MacEtch technique, optimizing the chemical solution and reaction conditions for the III-V semiconductor gallium arsenide (GaAs).

The process has two steps. First, a thin film of metal is patterned on the GaAs surface. Then, the semiconductor with the metal pattern is immersed in the MacEtch chemical solution. The metal catalyzes the reaction so that only the areas touching metal are etched away, and high-aspect-ratio structures are formed as the metal sinks into the wafer. When the etching is done, the metal can be cleaned from the surface without damaging it.

Pitt Researchers Propose New Model To Design Better Flu Shots

The flu shot, typically the first line of defense against seasonal influenza, could better treat the U.S. population, thanks to University of Pittsburgh researchers. New research that focuses on the composition and timing of the shot design was published in the September-October issue of Operations Research by Pitt Swanson School of Engineering faculty members Oleg Prokopyev, an assistant professor, and Professor Andrew Schaefer, both in the Department of Industrial Engineering, and coauthors Osman Ozaltin and Mark Roberts, professor and chair in Pitt's Department of Health Policy and Management. Ozaltin, who is now an assistant professor of engineering at the University of Waterloo in Ontario, did his research for the study as a Pitt graduate student in the Swanson School; he earned his Pitt PhD degree in industrial engineering earlier this year.

The exact composition of the flu shot is decided every year by the Food and Drug Administration (FDA), and the decision is complicated.

"The flu's high rate of transmission requires frequent changes to the shot," said Prokopyev. "Different strains can also cocirculate in one season, which gives us another challenge for figuring out the composition."

The Pitt researchers used powerful optimization methods from engineering to examine whether they could improve the yearly decisions made regarding what strains of influenza should be included in the current year's vaccine. The strains of flu that will be most likely to appear in the regular flu season are not known with certainty, but waiting longer to finalize the composition of the vaccine and observing what strains are occurring in other parts of the world improves the accuracy of the selection. However, the longer the FDA waits to make the decision, the more likely it is that there will be insufficient vaccine produced by the start of flu season. The model developed by the Pitt researchers balances these two important characteristics of the flu selection decision and integrates the composition and timing decisions of the flu shot design.

The model allows examination of the effect of many changes to the design and production of the vaccine, such as how many strains to include in the shot, when to make the final decision, how many times the FDA should meet to re-examine the current information concerning strains in other parts of the world, and the potential benefits from improved production methods.

"With this model, several policy questions can be addressed," said Schaefer. "For example, incorporating more than three strains might increase the societal benefit substantially, particularly under more severe flu seasons."

New Device Could Bring Optical İnformation Processing

Researchers have created a new type of optical device small enough to fit millions on a computer chip that could lead to faster, more powerful information processing and supercomputers. The "passive optical diode" is made from two tiny silicon rings measuring 10 microns in diameter, or about one-tenth the width of a human hair. Unlike other optical diodes, it does not require external assistance to transmit signals and can be readily integrated into computer chips.

The diode is capable of "nonreciprocal transmission," meaning it transmits signals in only one direction, making it capable of information processing, said Minghao Qi (pronounced Chee), an associate professor of electrical and computer engineering at Purdue University.

"This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing," said Qi, working with a team also led by Andrew Weiner, Purdue's Scifres Family Distinguished Professor of Electrical and Computer Engineering.

The diodes are described in a paper to be published online Dec. 22 in the journal Science. The paper was written by graduate students Li Fan, Jian Wang, Leo Varghese, Hao Shen and Ben Niu, research associate Yi Xuan, and Weiner and Qi.

Although fiberoptic cables are instrumental in transmitting large quantities of data across oceans and continents, information processing is slowed and the data are susceptible to cyberattack when optical signals must be translated into electronic signals for use in computers, and vice versa.

"This translation requires expensive equipment," Wang said. "What you'd rather be able to do is plug the fiber directly into computers with no translation needed, and then you get a lot of bandwidth and security."

Go To Work On A Christmas Card

If all the UK's discarded wrapping paper and Christmas cards were collected and fermented, they could make enough biofuel to run a double-decker bus to the moon and back more than 20 times, according to the researchers behind a new scientific study. The study, by scientists at Imperial College London, demonstrates that industrial quantities of waste paper could be turned into high grade biofuel, to power motor vehicles, by fermenting the paper using microorganisms. The researchers hope that biofuels made from waste paper could ultimately provide one alternative to fossil fuels like diesel and petrol, in turn reducing the impact of fossil fuels on the environment.

According to some estimates 1.5 billion cards and 83 square kilometres of wrapping paper are thrown away by UK residents over the Christmas period. They currently go to landfill or are recycled in local schemes. This amount of paper could provide 5-12 million litres of biofuel, say the researchers, enough to run a bus for up to 18 million km.

"If one card is assumed to weigh 20g and one square metre of wrapping paper is 10g, then around 38,300 tonnes of extra paper waste will be generated at Christmas time," said study author Dr Richard Murphy from the Department of Life Sciences at Imperial College London. "Our research shows that it would be feasible to build waste paper-to-biofuel processing plants that give energy back as transport fuel."

Co-author and PhD student Lei Wang, also from Imperial's Department of Life Sciences, said: "The fermentation process could even cope with festive paper and card which has been 'contaminated' with the likes of glitter and sellotape. The cellulose molecules in sellotape would be broken down into glucose sugars and then fermented into ethanol fuel, just like the paper itself. Insoluble items like glitter are easy to filter out as part of the process."

Dr Murphy added: "People should not stop recycling their discarded paper and Christmas cards because at the moment there is no better solution. However, if this technology can be developed further, waste paper might ultimately provide a great, environmentally friendly alternative to fossil fuels. There's more work to do to assess the effectiveness and benefits of the technology, but we think it has significant potential."

Shearing Triggers Odd Behavior İn Microscopic Particles

Microscopic spheres form strings in surprising alignments when suspended in a viscous fluid and sheared between two plates -- a finding that will affect the way scientists think about the properties of such wide-ranging substances as shampoo and futuristic computer chips. A team of scientists at Cornell University and the University of Chicago have imaged this behavior and have explained the forces causing it for the first time. Its findings appear in the Dec. 19-23 early edition of the Proceedings of the National Academy of Sciences.

"The experimental breakthrough revealed that these string structures were perpendicular to the shear instead of parallel to it, contrary to what many in the field were expecting," said Aaron Dinner, associate professor in chemistry at UChicago and a study co-author.

The experiment was led by Itai Cohen, associate professor of physics at Cornell, who custom-built a device that would enable him simultaneously to exert shearing forces on suspended colloids (the spheres) and image the resulting motion at 100 frames per second with a confocal microscope. Imaging speed was critical to the experiment because the string-like structures appear only at certain shear rates.

"This issue of strings has been pretty controversial. I'm not sure that we've solved all the controversies associated with them, but at least we've made a step forward," Cohen said.

Shearing forces affect the dynamic behavior of paint, shampoo and other viscous household products, but an understanding of these and related phenomena at the microscopic level has largely eluded a detailed scientific understanding until the last decade, Dinner noted.

Futuristically speaking, these forces potentially could be harnessed to produce microscopic patterns on computer chips or biosensors via special paints that flow easily when layered in one direction, but becomes hard when layered in another direction.

Cohen's objective was more scientifically immediate: to devise an experiment that would overcome the technical difficulties associated with measuring the mechanical properties of the colloidal strings while also imaging their formation. "The holy grail is to be able to understand how the structure leads to the mechanical properties and then to be able to control the mechanical properties by influencing the structure," Cohen explained.

Sunlight and Bunker Oil A Fatal Combination For Pacific Herring

The 2007 Cosco Busan disaster, which spilled 54,000 gallons of oil into the San Francisco Bay, had an unexpectedly lethal impact on embryonic fish, devastating a commercially and ecologically important species for nearly two years, reports a new study by the University of California, Davis, and the National Oceanic and Atmospheric Administration. The study, to be published the week of Dec. 26 in the early edition of the Proceedings of the National Academy of Sciences, suggests that even small oil spills can have a large impact on marine life, and that common chemical analyses of oil spills may be inadequate.

"Our research represents a change in the paradigm for oil spill research and detecting oil spill effects in an urbanized estuary," said Gary Cherr, director of the UC Davis Bodega Marine Laboratory and a study co-author.

On the foggy morning of Nov. 7, 2007, when the container ship collided with the San Francisco-Oakland Bay Bridge, bunker oil contaminated spawning habitats for the largest U.S. coastal population of Pacific herring -- a month before spawning season.

The new study, which analyzed Pacific herring embryos following the spill, highlights the effects of bunker oil on fish embryos in shallow water, the potential significance of sunlight interacting with oil compounds, and the extreme vulnerability of fish in early life stages to spilled oil.

Specifically, the study found that components of Cosco Busan bunker oil accumulated in naturally spawned herring embryos, then interacted with sunlight during low tides to kill the embryos. Laboratory-fertilized eggs, caged in deeper waters, were protected from the lethal combination of sunlight and oil, but still showed less severe abnormalities associated with oil exposure.

Crude oil is naturally occurring, liquid petroleum. Bunker oil is a thick fuel oil distilled from crude oil and burned on ships to fuel their engines. It is contaminated with various, sometimes unknown, substances.

The study builds on research following the 1989 Exxon Valdez spill, which released up to 32 million gallons of crude oil into the comparatively pristine environment of Prince William Sound, Alaska. That research established a new paradigm for understanding the effects of oil toxicity on fish at early life stages.

Irikaitz Archaeological Site Host To A 25,000-year-old Pendant

The recent discovery of a pendant at the Irikaitz archaeological site in Zestoa (in the Basque province of Gipuzkoa) has given rise to intense debate: it may be as old as 25,000 years, which would make it the oldest found to date at open-air excavations throughout the whole of the Iberian Peninsula. This stone is nine centimetres long and has a hole for hanging it from the neck although it would seem that, apart from being adornment, it was used to sharpen tools. This is one of a number of interesting findings made by the team led by Álvaro Arrizabalaga at this location: "Almost every year some archaeological artefact of great value is discovered; at times, even 8 or 10. It is a highly fruitful location."

Irikaitz lies behind the bath spa in Zestoa, on the other side of the river Urola, 14 metres from the river bank. The archaeologist from the University of the Basque Country (UPV/EHU) has been carrying out excavations here summer after summer, together with students and researchers from this and other universities and in cooperation with Aranzadi Science Society. Since 1998 they have uncovered 32 square metres; nothing compared to the eight hectares (at least) that this "gigantic" open-air site covers. This is archaeology, demanding a lot of patience, but the results are worth it: "You feel as if you have found something that has been waiting to fall into your hands for 200,000 years."

It is like a lottery

The tasks pertaining to an archaeological site are complex and lengthy in any case, but particularly so at Irikaiz. To start with, because it is in the open air. In the case of caves, it is known that they served as refuges for our ancestors and, once their location is identified, it is highly possible that archaeological treasures are found there. Open air archaeological sites, on the other hand, are discovered when some civil engineering infrastructure has to be built, and it is difficult to predict what will be found. Moreover, in Zestoa there are remains from the Lower Paleolithic, when there are hardly any references from this period in the Basque Country. According to Mr Arrizabalaga, when they started, "it was like a lottery. We did not know what to expect -- either about its chronology or about the kinds of remains likely to be uncovered."

Precisely because of this lack of references, they were fascinated when they came across "totally exotic" raw material: volcanic stones. "In the first dig, we thought at first that someone may have brought the rocks there when they were building the Urola railway, to use them as ballast. It was all so surprising and incredible," said the archaeologist. But no; this phenomenon had another logical explanation: "It is a geological rarity. In the Urola River valley there is a layer of volcanic stones; the river cut through these, took them to the surface and brought them to this place. This is why humans from prehistory came here -- there was no other place in the Basque Country with stones like these."

Brain's Connective Cells Are Much More Than Glue

Glia cells, named for the Greek word for "glue," hold the brain's neurons together and protect the cells that determine our thoughts and behaviors, but scientists have long puzzled over their prominence in the activities of the brain dedicated to learning and memory. Now Tel Aviv University researchers say that glia cells are central to the brain's plasticity -- how the brain adapts, learns, and stores information. According to Ph.D. student Maurizio De Pittà of TAU's Schools of Physics and Astronomy and Electrical Engineering, glia cells do much more than hold the brain together. A mechanism within the glia cells also sorts information for learning purposes, De Pittà says. "Glia cells are like the brain's supervisors. By regulating the synapses, they control the transfer of information between neurons, affecting how the brain processes information and learns."

De Pittà's research, led by his TAU supervisor Prof. Eshel Ben-Jacob, along with Vladislav Volman of The Salk Institute and the University of California at San Diego and Hugues Berry of the Université de Lyon in France, has developed the first computer model that incorporates the influence of glia cells on synaptic information transfer. Detailed in the journal PLoS Computational Biology, the model can also be implemented in technologies based on brain networks such as microchips and computer software, Prof. Ben-Jacob says, and aid in research on brain disorders such as Alzheimer's disease and epilepsy.

Regulating the brain's "social network"

The brain is constituted of two main types of cells: neurons and glia. Neurons fire off signals that dictate how we think and behave, using synapses to pass along the message from one neuron to another, explains De Pittà. Scientists theorize that memory and learning are dictated by synaptic activity because they are "plastic," with the ability to adapt to different stimuli.

But Ben-Jacob and colleagues suspected that glia cells were even more central to how the brain works. Glia cells are abundant in the brain's hippocampus and the cortex, the two parts of the brain that have the most control over the brain's ability to process information, learn and memorize. In fact, for every neuron cell, there are two to five glia cells. Taking into account previous experimental data, the researchers were able to build a model that could resolve the puzzle.

The brain is like a social network, says Prof. Ben-Jacob. Messages may originate with the neurons, which use the synapses as their delivery system, but the glia serve as an overall moderator, regulating which messages are sent on and when. These cells can either prompt the transfer of information, or slow activity if the synapses are becoming overactive. This makes the glia cells the guardians of our learning and memory processes, he notes, orchestrating the transmission of information for optimal brain function.

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