Scientific Journals

On the world, only two kinds of journals claiming publishing science can be found: (1) rubbish journals; (2) scientific journals.

Class (1) features papers filled with errors, trivial results or unjustified conclusions and claims, without rigorous peer review process;
Class (2) publishes papers of real scientific value (see the PRL acceptance criteria for reference).

One should always avoid class (1). Don't throw your thoughts in rubbish can.

In class (2), two categories can be seen: in (a) publish work on mainstream and hot topics, while in (b) publish work in non-mainstream subjects. Both are of scientific values, but interesting to different readers.

The mysterious Moire'- pattern-based electronic properties

Plenty of attention has been diverted to studying the bilayer graphene and hybrid structures consisting of patched mono-bi-layer graphene. A very fundamental problem in bi-layer graphene is how the electronic properties depend on the twisted angle. Theoretical study has been challenging. An interesting review in Nature on a recent PRL paper[http://www.nature.com/nature/journal/v474/n7352/full/474453a.html?WT.ec_id=NATURE-20110623#/references]:

In their study, Luican et al.⁴ find that, at small rotation angles, the local density of electronic states develops a dependence on position within the moiré-pattern unit cell and no longer exhibits the Dirac-like, decoupled-layer, Landau-level pattern. Layer coupling becomes strong in this sense for rotation angles less than about 2°, corresponding to moiré-pattern periods longer than about 10 nanometres. Here it is tempting to conjecture — from the spatial dependence of the density of electronic states — that bilayer wavefunctions have become localized, so that an STM measurement at one position reflects the stacking arrangement only at that position.
...
The extraordinary sensitivity of the electronic properties of few-layer graphene systems to the relative orientations of their layers could prove useful in various applications, for example in ultra-sensitive strain gauges, pressure sensors or ultra-thin capacitors. Further progress requires an improved understanding of both large and small rotation-angle limits, and also improved experimental control of rotation angles.

All organic molecule spin valve

I remember in my previous entry I mentioned a spin filtering effect of DNA molecules. Here comes another molecule with similar effect and can operate as a spin valve at low temperatures[http://www.nature.com/nmat/journal/v10/n7/full/nmat3061.html?WT.ec_id=NMAT-201107].

Now, writing in Nature Materials, Urdampilleta and co-workers¹ report that a single-walled carbon nanotube decorated with magnetic molecules can act in just the same way as a conventional spin valve, albeit only at low temperature.
...............
How is it possible for a single molecule to perform as efficiently as 10 nm of iron? The key is the ability of a chemical bond to modify the magnetic properties of a surface, which has been studied under the suggestive name of 'spinterface science'⁵. It has already been shown that an attached molecule can alter the spin-polarization of the electrons emerging from a magnetic surface^{6, 7}; the experiments of Urdampilleta and co-workers now prove the opposite effect — namely that a magnetic molecule can alter the spin polarization of the current flowing in a non-magnetic material. Two particular features make this possible. First, the magnetic centre must be sufficiently close to the conduction channel. In this respect, the case of bis-phthalocyaninato-terbium(III) is rather peculiar, because the Tb³⁺ ion (Tb³⁺ carries a total angular momentum, J = 6) is sandwiched between two phthalocyanine ligands, and it is at least 1 nm away from the nanotube — too far to transfer any magnetic information. However, there is a second source of spin in this molecule, namely a S = 1/2 radical delocalized over the two phthalocyanine ligands. These are likely to participate in the bond and help to spin-polarize the electron current. Second, the conduction channel must be sufficiently sensitive to the local magnetic moment. All the atoms in a single-walled carbon nanotube reside on the surface, so that a surface modification results in an alteration of the entire electronic structure. It is an extreme surface sensitivity that makes this spin valve work.

Noteworthy papers from latest issue of Science

1. Disorder-Enhanced Transport in Photonic Quasicrystals, 332:1541(2011);

Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals; examples of quasicrystals can be found in aluminum alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder.

2.Carbon-Based Supercapacitors Produced by Activation of Graphene, 332:1537(2011)

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp²-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

3. The Limits of Ordinary Matter, 332:1513(2011)

All ordinary matter consists of protons and neutrons, collectively called nucleons, which are bound together in atomic nuclei, and electrons. The elementary constituents of protons and neutrons, the quarks, almost always remain confined inside nucleons (or any other particle made up of quarks, called hadrons). The fundamental force that binds quarks together—the strong, or “color” force—cannot be overcome unless extremely high-energy conditions are created, such as through heavy-particle collisions. Theoretical simulations based on quantum chromodynamics (QCD) predict that the transition temperature for the appearance of free quarks should occur at 2.0 × 10¹² K (an energy of 175 million eV) (1, 2). Since 2000, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has created the necessary conditions to form quark matter in particle collision, but determining the transition temperature under these conditions is challenging. On page 1525 of this issue, Gupta et al. (3) show that the relevant temperature and energy scales can be extracted from recent experimental studies and find that the transition temperature is in remarkable agreement with theory.

4 This paper is not published in Science, but highlighted in it: Nano Lett. 11, 10.1021/nl200928k (2011).

It has long been known from ex situ studies that metal nanoparticles can catalyze reaction of oxygen with graphite surfaces and create grooves or channels. Such reactions could be used for patterning graphene sheets. Booth et al. have studied the dynamics of silver nanoparticles on suspended monolayer and bilayer graphene sheets in a transmission electron microscope. They imaged these samples at temperatures from 600 to 850 K and partial pressures of oxygen over the sample from about 30 to 100 millitorr. The nanoparticles cut channels along <100> crystallographic directions, but some fluctuations of motion normal to the channel direction were also observed. The nanoparticles did not move at a constant speed. Instead, their velocity profile was erratic, and the start-stop motion was better described by a Poisson distribution.

News from this issue of Science Magazine

1. Batteries are going to break out from old forms:

Now he's on his way. Last month, Chiang and his colleagues reported in Advanced Energy Materials that they've created a new battery design called a semisolid flow cell that's like a battery with a fuel tank. Like today's batteries, the device contains lithium ions that shuttle back and forth either storing or releasing electrical charges on demand. But instead of packaging those ions along with the electrodes and other apparatus all together, as in a typical battery, Chiang's semisolid flow cell separates the energy-delivery apparatus from energy storage. In this battery, the storage medium is a pair of gooey, black liquids, the consistency of yogurt, that contain nanoscale particles of materials commonly used as anodes and cathodes in lithium-ion cells. These particles are suspended in an electrolyte and separated by a porous membrane. When power is needed, a bolus of each goo is pumped from external tanks into a network of current collectors that extract electrons while lithium ions shuttle through the membrane from the anode particles to the cathode particles. The spent slurries can then be reenergized, as in a normal rechargeable battery, or pumped out and replaced. Other types of flow batteries have been made in the past, but Chiang says the new setup can store up to 30 times as much energy as previous versions. He has launched another company, called 24M, to commercialize the technology.[http://www.sciencemag.org/content/332/6037/1494.full]

2.

Move over, China. Japan's “K Computer” is now the fastest supercomputer in the world. On 20 June, K was ranked number one in the TOP500 list of the world's supercomputers, performing three times as fast as its Chinese rival and the previous champion, Tianhe-1A.

The TOP500 list is updated twice a year and ranks how quickly computers solve a standard mathematical equation. K, built by Fujitsu and located at the RIKEN Advanced Institute for Computational Science in Kobe, can perform 8.2 quadrillion calculations per second, equivalent to linking about 1 million desktop computers. That performance is still shy of the target kei, or 10 quadrillion, calculations for which the supercomputer was named. This is the first time Japan has topped the list since 2004.[http://www.sciencemag.org/content/332/6037/1488.2.full]

3. Education is not a rece:

In the United States and elsewhere, the competitive pressures placed on young people in school are damaging many otherwise promising lives. In addition to generating debilitating anxiety and encouraging a culture of cheating, this competition takes the joy out of learning. The film Race to Nowhere, which continues to receive attention since its release a year ago, documents the unhealthy consequences of the competitive “teach to the test” climate that many U.S. students experience. The film, in which I was interviewed, puts in clear relief the pressures that youth are under to amass large numbers of Advanced Placement (college-equivalent) classes, win science fairs, excel in the arts and sports, and in other ways distinguish themselves from the competition for admission into a few select universities that parents and schools believe are critical for future success. Research on motivation makes it clear that focusing attention entirely on performance, whether grades or test scores, destroys whatever intrinsic interest the subject matter might have had.* There are certainly students whose passions spur them to realize their full potential in rigorous academic courses and other impressive activities. But how many potential Nobel Prize winners have written off science before the end of high school because their only exposure to the subject had been in test preparation courses rather than in classes that delved into meaningful questions? It doesn't have to be this way, but change will require coordinated efforts at many levels.

Success in life does not require a degree from one of 10 universities. We need to evaluate U.S. high schools (pre-college education) on how well they help students find a college that matches their interests and goals, not on the proportion of students that they send to elite institutions. And the coveted universities need to demonstrate that they are interested in students who have a genuine passion for extending their educational experience, not merely in tallying items on resumés.

Many U.S. teachers also must change their approach to teaching. Extensive research shows that students will become more emotionally engaged (and even passionate) if simple principles are followed: if the subject matter is connected to students' personal lives and interests; if students have opportunities to be actively involved in solving or designing solutions to novel and multidimensional problems, doing experiments, debating the implications of findings, or working collaboratively; if students have multiple opportunities to earn a good grade (by rewriting papers or retaking tests); if attention is drawn to the knowledge and skills that students are developing, not to grades or scores; and if all learning and skill development is celebrated, whatever the level.

Schools must create homework policies to ensure that diligent students aren't kept up late into the night; schedule some spacing between major tests and offer ample opportunities for students to get extra help; make sure that at least one adult is paying attention to every student's emotional needs; provide parent education on the advantages of a broad array of potential colleges; survey students regularly on the sources of their stress and make sure that this feedback informs policies; and offer opportunities for students to pursue academic interests unencumbered by performance concerns, such as in independent studies or clubs.

The world is rapidly changing. Problem-solving skills and critical analysis have become infinitely more important than being able to answer the typical questions given on standardized tests. A valuable science of teaching and learning exists that should guide efforts to improve students' interest, engagement, and intellectual skills, as well as reduce the debilitating stress that is becoming epidemic.** Only by paying attention to what we know can we make the changes that youth need to lead healthy and productive lives. [http://www.sciencemag.org/content/332/6037/1481.full]

Einstein's Theory STANDS UP

Usually quoted as the most refined brain child ever seen in human history, Einstein's general relativity theory has been frequently under test and it passed. The latest test was initiated some half a century ago and eventually came up with a result: it passed again ! [http://www.physicstoday.org/daily_edition/physics_update/gravity_probe_b_concludes_its_50-year_quest]

Results of an experiment conceived around 1960 to test general relativity and launched in 2004 were announced at a NASA press conference earlier this month: Albert Einstein’s theory passed. The experiment featured four (for redundancy) gyroscopes—spinning, niobium-covered spheres—orbiting 642 km above Earth (see the figure). The goal was to measure the precession induced in the gyroscopes by two general relativistic effects. The easier-to-measure geodetic effect influences any spinning object orbiting a mass. The second effect, frame dragging, arises when the spacetime-distorting mass, here Earth, is itself spinning. Gravity Probe B was not the first to measure the two effects, but it was designed to measure them independent of each other and to extraordinary precision. The gyroscopes are the most perfectly spherical objects ever fabricated. They needed to be, lest the general relativistic precessions be swamped by those arising from Newtonian torques. To measure the spin of those featureless spheres, the experimenters cooled them below niobium’s superconducting transition; the superconducting metal then produces a magnetic field, parallel to its spin axis, that can be measured with a superconducting quantum interference device. In the end, the experiment was a qualified success. It measured the geodetic effect to 0.3% precision, but stray charges on the gyroscopes and their housings limited the precision of the frame-dragging measurement to 20%. In both cases other efforts have achieved comparable results. (C. W. F. Everitt et al., Phys. Rev. Lett., in press.)—Steven K. Blau

How do wings work ?

This is an interesting article from the wonderful journal I posted in my last entry. It tries to poke the usual (even textbook) explanation of how wings work [2003 Phys. Educ. 38: 497].

Now Bernoulli’s equation is quoted, which states that larger velocities imply lower pressures and thus a net upwards pressure force is generated. Bernoulli’s equation is often demonstrated by blowing over a piece of paper held between both hands as demonstrated in figure 2. As air is blown along the upper surface of the sheet of paper it rises and, it is said, this is because the average velocity on the upper surface is greater (caused by blowing) than on the lower surface (where the air is more
or less at rest). According to Bernoulli’s equation this should mean that the pressure must be lower above the paper, causing lift. The above explanation is extremely widespread. It can be found in many textbooks and, to my knowledge, it is also used in the RAF’s instruction manuals. The problem is that, while it does contain a grain of truth, it is incorrect in a number of key places.

What’s wrong with the ‘popular’ explanation?
The distance argument;
The ‘equal time’ argument;
The Bernoulli demonstration.

Next, examine a particle moving along a curved streamline as shown in figure 7. For simplicity we can assume that the particle’s speed is constant3. Because the particle is changing direction there must exist a centripetal force acting normal to the direction of motion. This force can only be generated by pressure differences (all other forces are ignored), which implies that the pressure on one side of the particle is greater than that on the other. In other words, if a streamline is curved, there must be a pressure gradient across the streamline, with the pressure increasing in the direction away from the centre of curvature.