# Editors' Choice

Science  23 Dec 2011:
Vol. 334, Issue 6063, pp. 1605
1. Education

# Calling Out Cash Incentives

The English writer Hazlitt claimed “Learning is its own exceeding great reward.” Economists argue that increased lifetime earnings are a more powerful prize for the educated. Kindergarten teachers know the motivational magic of a simple “Good job!” Whatever their form, rewards and education go hand in hand. Fryer examined whether direct financial payments could improve outcomes in low-performing urban schools. Randomized 2-year trials included roughly 27,000 students in 203 public schools located in three cities. Dallas 2nd-graders received $2 per book read, New York City 4th- and 7th-graders earned up to$50 for performance on certain tests, and Chicago 9th-graders earned up to $50 for class grades.$9.4 million was distributed, with impacts measured on city-specific achievement tests. English-speaking students in Dallas improved, whereas English-language learners were hindered, relative to controls. Rewarding the reading of English-language books may have “crowded out” academic Spanish, hindering low-performing Spanish-speakers being provided with intense Spanish remediation. Other than this subsample, the overall impact of incentives was statistically zero. However, Fryer noted that the study was not designed to detect small-to-modest effect sizes, and the 95% confidence intervals contained effect sizes that could still return up to 5% on investment. Rewarding “inputs” to learning (such as reading books) may be better than focusing on “outputs” (such as test scores), because students may not know how best to translate efforts into outcomes.

Q. J. Econ. 126, 1755 (2011).

2. Applied Physics

# Integrated Quantum Optics

1. Ian S. Osborne

Applications based on quantum optics depend on the ability to produce and detect single photons and to reliably send them around circuits where the information they carry can be manipulated. Most approaches to date have been modular, with photon production, detection, and manipulation being separate elements. The poor coupling between these separate elements incurs high losses that render reliable applications impractical. Gerrits et al. have developed an integrated approach that combines a superconducting transition edge sensor capable of resolving individual photons with a silica optical waveguide. The integrated on-chip approach results in low losses for the photons and therefore presents a feasible route toward scalable photonic quantum processing devices that are sufficiently complex to be useful in applications such as quantum computing, metrology, and simulation.

Phys. Rev. A 84, 60301R (2011)

3. Materials Science

# Dimeric Dopants

1. Phil Szuromi

Just as with inorganic semiconductors, dopants can improve the conductivity of organic electronic materials. Alkali metals have been used as electron-donating (n-type) dopants, but they can diffuse through the material and can create charge trapping sites. Strongly reducing molecular n-dopants are attractive alternatives but are generally too air-sensitive for practical use. Guo et al. show that the dimeric forms of cyclopentadienyl-type sandwich compounds, such as the dimeric form of rhodocene and (pentamethylcyclopentadienyl)ruthenium(1,3,5-trialkylbenzene) (where alkyl can be methyl or ethyl), are moderately air-stable in the solid state. With solid-state electron affinities as low as 2.8 eV, these compounds can be used to n-dope a variety of electron-transport materials both in solution and in the vapor phase. The rhodocene dimer was used as the n-dopant for copper phthalocyanine in a p-i-n homojunction diode that achieved a rectification ratio of greater than 106 at a bias of 4 V.

4. Astronomy

# A Clear View in the IR

1. Maria Cruz

If human eyes were sensitive to light in the infrared (IR) instead of the optical regime, the night sky would not appear dark to us. That's because hydroxyl molecules in the atmosphere emit IR light in the form of a forest of extremely bright, very narrow emission lines. This light varies very rapidly and would prevent us from seeing much of the universe beyond Earth, apart from the Sun, the Moon, a few planets, and possibly a few stars. To overcome this problem, astronomers launch IR telescopes into space. However, space telescopes are expensive, and have limited apertures and long lead times. Bland-Hawthorn et al. describe a filter that is capable of suppressing the atmospheric IR lines and can be used on ground-based telescopes. The filtering process involves focusing light onto an optical fiber and splitting it into parallel tracks, using what is termed photonic lantern technology. Each track is then processed by a Bragg filter, a device that reflects back the light from the atmospheric emission lines and lets wavelengths between those lines through. This setup was successfully tested at Siding Spring Observatory in New South Wales, Australia.

Nat. Commun. 2, 10.1038/ncomms1584 (2011).

5. Cell Biology

# Full of Holes

1. Stella M. Hurtley

The endothelium acts as a barrier between tissues, but can sometimes be transiently perforated in health and disease by transcellular tunnels. These tunnels can allow the passage of leukocytes to sites of infection, but can also be exploited by invading pathogens. Maddugoda et al. studied the effects of the edema toxin (ET) from Bacillus anthracis on endothelial integrity. In mice, intravascular injection of ET led to an increase in endothelial permeability and the generation of transcellular tunnels via its effects on cyclic-AMP signaling. After this permeabilization, the transcellular tunnels were “healed” by the action of the MIM (Missing in Metastasis) protein, which, in response to the increased membrane curvature induced by the tunnels, triggered the production of actin-rich membrane protrusions that seal the tunnel. This type of transient permeabilization and resealing of the endothelial barrier probably regulates the overall permeability of the endothelium, and perturbation of this balance by the action of pathogens can be key to their successful colonization of the host.

Cell Host Microbe 10, 464 (2011).

6. Physics

# Mimicking Magnets

1. Jelena Stajic

When a solid with electrons confined to two dimensions is placed in a magnetic field at low temperature, its transverse electrical conductivity may become quantized; this collective phenomenon is known as the quantum Hall effect (QHE). Because solid-state systems in which QHE occurs are limited by their material properties, it is desirable to simulate the effect in a more tunable and less disordered context, such as a cold atomic gas placed in an optical lattice. However, neutral atoms are not affected by a magnetic field the way electrons are. Experimenters previously found a way around that issue by creating an effective magnetic field analogue through rotating the gas, or applying Raman lasers, but the interesting strong field regime had not been reached. Now, Aidelsburger et al. have placed an ultracold gas in a two-dimensional optical lattice where the potential was staggered in one direction, leading to suppressed tunneling. Tunneling was recovered through coupling to a pair of Raman lasers, but as a consequence, the tunneling atoms' wave functions acquired a phase equivalent to the presence of a strong magnetic field. The strength of the field could be tuned by changing the angle between the lasers, and its presence was confirmed through the cyclotron-like orbits of the atoms.

Phys. Rev. Lett. 107, 255301 (2011).

7. Plant Science

# Root Growth Revealed

1. Pamela J. Hines

In the growing Arabidopsis root tip, the hormone auxin regulates cell division and differentiation from the stem cell niche. Auxin is expressed as a gradient, which peaks at the root meristem, where stem cells drive root growth. This asymmetry is maintained by transporter proteins that are themselves asymmetrically organized to transport auxin from cell to cell. The gene BREVIS RADIX (BRX), which is regulated by auxin, does not, however, function in a pattern that reflects the auxin distribution. Through a combination of experiment and dynamic computational modeling to describe the interactions of hormone and targets, Santuari et al. found out why. The BRX gene appeared to encode a transcriptional coregulator despite BRX primarily localizing to the plasma membrane. Because BRX function in the nucleus is dependent on endocytic recycling, the authors layered endocytosis pathways into their computational model. The endocytic pathways themselves respond to auxin, although in a nonlinear manner. By combining the various inputs, the authors generated a model that reflected BRX function in the normal root. Thus, although auxin regulates BRX transcription, the association of BRX with the plasma membrane, and the activity of the endocytic pathways required to get BRX to the nucleus, add up to a cellular distribution of BRX that does not parallel the distribution of auxin.

Curr. Biol. 21, 1918 (2011).