bluuebunny/crossref_metadata_2025 huggingface dataset:
The Seabots are Coming Here: Should they be Treated as ‘Vessels’?
Authors: Allen Craig H.
Published: May 2012

Unmanned Marine Vehicles (UMVs), like their aerial cousins Unmanned Aerial Vehicles (UAVs), are not easily classified under existing legal regimes. Even though unmanned, should these seagoing drones be treated as ‘vessels’ under the Law of the Sea Convention articles on navigation rights and duties? Are they ‘vessels’ under the International Regulations for Preventing Collisions at Sea (COLREGs, 1972)? If so, should they be accorded a manoeuvring priority vis-à-vis other vessels? Are the differences between autonomous UMVs and the increasingly automated manned vessels all that great, such that classification should turn on whether the vessel is manned rather than on how navigation and collision avoidance decisions are made and executed?
A few comments on ‘Sustainability and the measurement of wealth’
Authors: Solow Robert
Published: May 2012

You have to admire the courage exhibited in going out on a limb like this, especially because the acrobats are sophisticated and understand how many chances to go wrong they have. Of course one can stand back and admire courage and dexterity without actually believing in the results, and without any feeling that one could do better.
Evidence on the prevalence and geographic distribution of major cardiovascular risk factors in Italy
Authors: Laccetti Roberta , Pota Andrea , Stranges Saverio , Falconi Claudio , Memoli Bruno , Bardaro Leopoldo , Guida Bruna
Published: May 2012

Objective

To assess the prevalence and geographic distribution of major cardiovascular risk factors in a large community-wide sample of the Italian population.

Design

A cross-sectional survey. Standardized methods were used to collect and measure cardiovascular risk factors. Data were adjusted for survey weightings. Qualitative and quantitative variables were compared with parametric and non-parametric tests, as appropriate.

Setting

Towns (n 193) across different Italian regions.

Subjects

Unselected adults (n 24 213; 12 626 men; 11 587 women) aged 18–98 years (mean age 56·9 (sd 15·3) years), who volunteered to participate in a community-wide screening programme over a 2 d period in 2007.

Results

Overall, the prevalence of major cardiovascular risk factors was: obesity, 22·7 % (women 18·9 %, men 26·1 %); overweight, 44·7 % (women 31·6 %, men 56·7 %); hypertension, 59·6 % (women 48·3 %, men 70·0 %); dyslipidaemia, 59·1 % (women 57·7 %, men 60·3 %); diabetes, 15·3 % (women 11·2 %, men 19·0 %) and smoking, 19·8 % (women 14·0 %, men 25·2 %). We found a high prevalence of unhealthy eating habits; fruit and vegetable consumption was below the recommended range in 60 % of the study population. Ninety per cent of the study population had more than one cardiovascular risk factor and 84 % had between two and five cardiovascular risk factors. There were differences among Italian macro-areas mainly for obesity, hypertension, dyslipidaemia and diabetes.

Conclusions

The study provides alarming evidence on current prevalence data for major cardiovascular risk factors in a large sample of the Italian population. Particularly, obesity and hypertension represent a relevant public health problem. There is a pressing need for effective preventive health measures which must also take into account the differences among Italian macro-areas.
Water vapor feedback in a small ensemble of GCMs: Two approaches
Authors: Ingram W. J.
Published: May 2012

The clear‐sky longwave component of the climate sensitivity parameterλCSLWis estimated for 5 diverse state‐of‐the‐art general circulation models (GCMs). A common radiation code is used to calculate 2 alternative breakdowns. The conventional breakdown, into “surface temperature feedback”, “lapse rate feedback” and “water vapor feedback” shows only the well‐known result of large but mostly compensating variations in the latter two components, due to variations in the distribution of warming. In one GCM,λCSLW is rather stronger than the rest, tending to reduce the sensitivity of climate. The “partly Simpsonian” breakdown shows that this is because of a combination of having less water vapor to start with and less increase in water vapor around the tropopause on warming. Two GCMs show λCSLWrather weaker than the rest, because of weaker amplification of the warming aloft, in one case combined with stronger‐than‐average relative humidity increases. The net effect of greater lapse rate changes (proportionally more warming aloft) can be seen to tend consistently to reduce climate sensitivity slightly. Also, though the impact of relative humidity changes is dominated by reductions through most of the depth of the troposphere, its variation across GCMs is dominated by increases around the tropopause. While the results from so small a sample will not be quantitatively general, they suggest that applying the new breakdown to a much wider range of GCMs would give useful quantitative and physical information on the variation ofλCSLW across current GCMs.
Potential impact of initialization on decadal predictions as assessed for CMIP5 models
Authors: Branstator Grant , Teng Haiyan
Published: May 2012

To investigate the potential for initialization to improve decadal range predictions, we quantify the initial value predictability of upper 300 m temperature in the two northern ocean basins for 12 models from Coupled Model Intercomparison Project phase 5 (CMIP5), and we contrast it with the forced predictability in Representative Concentration Pathways (RCP) 4.5 climate change projections. We use a recently introduced method that produces predictability estimates from long control runs. Many initial states are considered, and we find on average 1) initialization has the potential to improve skill in the first 5 years in the North Pacific and the first 9 years in the North Atlantic, and 2) the impact from initialization becomes secondary compared to the impact of RCP4.5 forcing after 6 1/2 and 8 years in the two basins, respectively. Model‐to‐model and spatial variations in these limits are, however, substantial.
Attribution of the summer warming since 1970s in Indian Ocean Basin to the inter‐decadal change in the seasonal timing of El Niño decay phase
Authors: Li Qian , Ren R.‐C. , Cai M. , Wu G. X.
Published: May 2012

This paper reports that, on top of the general warming trend in the Indian Ocean Basin (IOB) SST in the past 140 years, there exists an additional multidecadal‐scale warming in the period from late 1940s to early 2000s, and this warming in IOB is particularly stronger in summer than in other seasons. Our analysis indicates that, the seasonal timing of the decay phase of El Niño events during this period has been delayed from spring to early summer since 1970s, while the seasonal timing of La Niña decay phase remains in spring season. The direct effect of the later decay of El Niño events is the lengthening of the delayed warming effect of El Niño on IOB SST into summer, attributing to the stronger IOB warming in summer from the late 1940s to the early 2000s.
Multielectron redox chemistry of lanthanide Schiff-base complexes
Authors: Camp Clément , Guidal Valentin , Biswas Biplab , Pécaut Jacques , Dubois Lionel , Mazzanti Marinella
Published: May 2012

We have developed a new way to introduce redox events at lanthanide centers which should lead to further expansion of the reductive chemistry of lanthanides.
Current-voltage characteristics of the double tunnel junctions Co2CrAl–I–Pb/Sn–I–Pb under spin-polarized tunnel injection
Authors: Rudenko E. M. , Korotash I. V. , Krakovnyi A. A. , Dyakin M. V. , Dubina D. S. , Solomakha D. A.
Published: May 2012

Current-voltage characteristics and existence features of a superconducting state under the action of tunneling injection of the spin-polarized current Iinj with a high spin polarization degree (p ≈ 0.97) were studied in double tunneling junctions ferromagnet-insulator-superconductor-insulator-superconductor Co2CrAl–I–Pb/Sn–I–Pb. An empirical formula was proposed for describing a dependence of the energy gap Δ on Iinj. A new spin-polarized inhomogeneous superconducting state consisting of superconducting and resistive regions was found. An existence of the proximity effect through a tunnel barrier between ferromagnetic and superconducting films was established. An effective recombination time of spin-polarized quasiparticles in the nonequilibrium superconductor Pb was estimated.
Efros-Shklovskii variable range hopping transport in nanocluster metallic films
Authors: Abraham Thejal , Bansal Chandrahas , Kumaran J. Thampi Thanka , Chatterjee Ashok
Published: May 2012

It is shown that a film composed of nanoclusters of metal alloys of magnetic materials with a small oxide shell exhibits a Coulomb gap behaviour and the electronic transport in these nanostructured systems is governed by a variable range hopping mechanism as given by the Efros-Shklovskii model. This interesting observation is likely to have far-reaching consequences in several transport-related behaviour in micro-electronics of nano-clusters and in ultra-high density data storage devices and is expected to have a great impact on the new generation magnetic recording media and magnetic sensors made out from these clusters.
On the effects of mass and momentum transfer from droplets impacting on steady two-dimensional rimming flow in a horizontal cylinder
Authors: Williams J. , Hibberd S. , Power H. , Riley D. S.
Published: May 2012

Motivated by applications in aero-engines, steady two-dimensional thin-film flow on the inside of a circular cylinder is studied when the film surface is subject to mass and momentum transfer from impacting droplets. Asymptotic analysis is used systematically to identify distinguished limits that incorporate these transfer effects at leading order and to provide a new mathematical model. Applying both analytical and numerical approaches to the model, a set of stable steady, two-dimensional solutions that fit within the rational framework is determined. A number of these solutions feature steep fronts and associated recirculating pools, which are undesirable in an aeroengine since oil may be stripped away from the steep fronts when there is a core flow external to the film, and recirculation may lead to oil degradation. The model, however, provides a means of investigating whether the formation of the steep fronts on the film surface and of internal recirculation pools can be delayed, or inhibited altogether, by designing jets to deliver prescribed distributions of oil droplets or by the judicious siting of oil sinks. Moreover, by studying pathlines, oil-residence times can be predicted and systems optimized.
Supersonic gas jets for laser-plasma experiments
Authors: Schmid K. , Veisz L.
Published: May 2012

We present an in-depth analysis of De Laval nozzles, which are ideal for gas jet generation in a wide variety of experiments. Scaling behavior of parameters especially relevant to laser-plasma experiments as jet collimation, sharpness of the jet edges and Mach number of the resulting jet is studied and several scaling laws are given. Special attention is paid to the problem of the generation of microscopic supersonic jets with diameters as small as 150 μm. In this regime, boundary layers dominate the flow formation and have to be included in the analysis.
Stress-based resonant volatile gas microsensor operated near the critically buckled state
Authors: Joe Daniel J. , Linzon Yoav , Adiga Vivekananda P. , Barton Robert A. , Kim Moonkyung , Ilic Bojan , Krylov Slava , Parpia Jeevak M. , Craighead Harold G.
Published: May 2012

We describe sensing of chemical vapors from the atmosphere using critically buckled polycrystalline silicon doubly clamped mechanical resonators coated on one side with polymethyl methacrylate (PMMA). Our method of sensing is based on stress-induced resonance frequency shifts through volumetric swelling of the 60 nm thick PMMA layer resulting in altered tension in the beams. The stress change produces shifts in the resonance frequency as large as 150% of the baseline frequency. In order to maximize the sensitivity, we tailor residual stress of the polycrystalline silicon resonators to slightly exceed the critical buckling stress. We incorporate a relatively large gap between the bridge and a substrate to provide optical readout and minimize squeezed film effects. We show that the larger gap results in substantial improvements of the quality factor and frequency stability of our resonators under ambient pressure and temperature conditions compared to previous implementations. These lead to resonance frequency shift per concentration change of ethanol vapors of ∼360 Hz/ppm with a response time of a few seconds measured in our gas delivery and readout system.
Nanometer-size anisotropy of injection-molded polymer micro-cantilever arrays
Authors: Urwyler Prabitha , Deyhle Hans , Bunk Oliver , Magnus Kristiansen Per , Müller Bert
Published: May 2012

Understanding and controlling the structural anisotropies of injection-molded polymers is vital for designing products such as cantilever-based sensors. Such micro-cantilevers are considered as cost-effective alternatives to single-crystalline silicon-based sensors. In order to achieve similar sensing characteristics, structure and morphology have to be controlled by means of processing parameters including mold temperature and injection speed. Synchrotron radiation-based scanning small- (SAXS) and wide-angle x-ray scattering techniques were used to quantify crystallinity and anisotropy in polymer micro-cantilevers with micrometer resolution in real space. SAXS measurements confirmed the lamellar nature of the injection-molded semi-crystalline micro-cantilevers. The homogenous cantilever material exhibits a lamellar periodicity increasing with mold temperature but not with injection speed. We demonstrate that micro-cantilevers made of semi-crystalline polymers such as polyvinylidenefluoride, polyoxymethylene, and polypropylene show the expected strong degree of anisotropy along the injection direction.
Quantum continuum mechanics made simple
Authors: Gould Tim , Jansen Georg , Tokatly I. V. , Dobson John F.
Published: May 2012

In this paper we further explore and develop the quantum continuum mechanics (QCM) of Tao et al. [Phys. Rev. Lett. 103, 086401 (2009)] with the aim of making it simpler to use in practice. Our simplifications relate to the non-interacting part of the QCM equations, and primarily refer to practical implementations in which the groundstate stress tensor is approximated by its Kohn-Sham (KS) version. We use the simplified approach to directly prove the exactness of QCM for one-electron systems via an orthonormal formulation. This proof sheds light on certain physical considerations contained in the QCM theory and their implication on QCM-based approximations. The one-electron proof then motivates an approximation to the QCM (exact under certain conditions) expanded on the wavefunctions of the KS equations. Particular attention is paid to the relationships between transitions from occupied to unoccupied KS orbitals and their approximations under the QCM. We also demonstrate the simplified QCM semianalytically on an example system.
Mechanism of A-B intersite charge transfer and negative thermal expansion in A-site-ordered perovskite LaCu3Fe4O12
Authors: Li Hongping , Lv Shuhui , Wang Zhongchang , Xia Yanjie , Bai Yijia , Liu Xiaojuan , Meng Jian
Published: May 2012

Temperature induced intermetallic charge transfer and negative thermal expansion in compounds hold promise for many applications. Here, we report, by the first-principles calculations, the mechanism behind these effects and the associated electrical and magnetic properties of an A-site-ordered perovskite LaCu3Fe4O12. We find that the sensitive expansion of Cu-O bonds to temperature can trigger a transformation from Cu3+ to Cu2+, which imposes a covalent state transition of B-site Fe from +3 to +3.75. The resultant shrinkage of the Fe-O bonds is demonstrated to play a pivotal role in the volume contraction of the oxide at high temperatures.
Nanohole pattern formation on germanium induced by focused ion beam and broad beam Ga+ irradiation
Authors: Fritzsche Monika , Muecklich Arndt , Facsko Stefan
Published: May 2012

Hexagonally ordered nanohole patterns were produced on Ge(100) surfaces by focused Ga+ ion beam and broad Ga+ ion beam irradiations with 5 keV energy under normal incidence. Identical patterns were obtained by irradiations with a scanning focused ion beam under different irradiation conditions and with a broad Ga+ beam without scanning and five orders of magnitude smaller ion flux. Thus, we could demonstrate that nanohole pattern formation is independent of ion flux over several orders of magnitude and scanning of a focused ion beam under appropriate conditions is identical to broad ion beam irradiation.
Dependence of chaotic diffusion on the size and position of holes
Authors: Knight Georgie , Georgiou Orestis , Dettmann Carl P. , Klages Rainer
Published: May 2012

A particle driven by deterministic chaos and moving in a spatially extended environment can exhibit normal diffusion, with its mean square displacement growing proportional to the time. Here, we consider the dependence of the diffusion coefficient on the size and the position of areas of phase space linking spatial regions (‘holes’) in a class of simple one-dimensional, periodically lifted maps. The parameter dependent diffusion coefficient can be obtained analytically via a Taylor-Green-Kubo formula in terms of a functional recursion relation. We find that the diffusion coefficient varies non-monotonically with the size of a hole and its position, which implies that a diffusion coefficient can increase by making the hole smaller. We derive analytic formulas for small holes in terms of periodic orbits covered by the holes. The asymptotic regimes that we observe show deviations from the standard stochastic random walk approximation. The escape rate of the corresponding open system is also calculated. The resulting parameter dependencies are compared with the ones for the diffusion coefficient and explained in terms of periodic orbits.
Nuclear spin depolarization via slow spin diffusion in single InAlAs quantum dots observed by using erase-pump-probe technique
Authors: Adachi S. , Kaji R. , Furukawa S. , Yokoyama Y. , Muto S.
Published: May 2012

Nuclear spin diffusion in single self-assembled InAlAs quantum dots was studied by using erase-pump-probe technique. As a measure of nuclear spin polarization, transients of the Overhauser shift (OHS) of positive trion were probed in the respective pulse region. The achieved stable OHS was relaxed with a long depolarization time as long as a few tens of seconds and a diffusion constant of ∼5 × 10−15 cm2/s was estimated. The slow transfer of the spin energy is considered to be due to the dipole-dipole interaction of the nuclei. In addition, through the magnetic field dependence of OHS, the stability of the nuclear spin polarization was briefly discussed, and the saturated maximum values of OHS were investigated experimentally.
A high-pressure far- and mid-infrared study of 1,1-diamino-2,2-dinitroethylene
Authors: Pravica Michael , Liu Yu , Robinson John , Velisavljevic Nenad , Liu Zhenxian , Galley Martin
Published: May 2012

High pressure infrared (IR) measurements of the insensitive explosive, 1,1-diamino-2,2-dinitroethylene (DADNE or FOX-7), have been performed in the far- and mid-IR spectral regions up to ∼28 GPa using a synchrotron source. Petroleum jelly and KBr were employed as the pressurizing media for the far- and mid-IR experiments, respectively. In both experiments, IR spectra were collected at various pressures both in compression and decompression to determine reversibility under pressure cycling. There is evidence for at least two and possibly three phase transitions in the samples at pressures near 2, 5, and10 GPa, respectively. In the high frequency region (∼3000–3300 cm−1), the NH2 symmetric and antisymmetric vibrational modes soften with increasing pressure, suggesting strengthening intermolecular hydrogen bonding, and then stiffen with further pressure increase. At higher pressures (above 5 GPa), we suspect progressive flattening of the zig zag structure characteristic of the α phase occurs, which was observed in the low temperature, quenched γ phase. FOX-7 was also observed to survive pressure cycling up to 28 GPa contrary to earlier reports of pressure-induced molecular decomposition.
Switching performance of a polymer-stabilized antiferroelectric liquid crystal based on bent-core molecules
Authors: Atorf B. , Hoischen A. , Ros M. B. , Gimeno N. , Tschierske C. , Dantlgraber G. , Kitzerow H.
Published: May 2012

Mixtures of a non-reactive and a photo-reactive liquid crystal, both consisting of bent core molecules, were used to prepare polymer-stabilized antiferroelectric liquid crystal cells by in-situ photo-polymerization. The mixtures exhibit a larger temperature range of the antiferroelectric phase than the pure compounds. The polymer network improves the ability of uniform alignment and thus enhances the switching contrast. In addition, the polymer-network reduces the switching times, in particular the relaxation time from the field-induced state to the ground state.
Probing buried layers by photoelectron spectromicroscopy with hard x-ray excitation
Authors: Wiemann C. , Patt M. , Cramm S. , Escher M. , Merkel M. , Gloskovskii A. , Thiess S. , Drube W. , Schneider C. M.
Published: May 2012

We report about a proof-of-principle experiment which explores the perspectives of performing hard x-ray photoemission spectromicroscopy with high lateral resolution. Our results obtained with an energy-filtered photoemission microscope at the PETRA III storage ring facility using hard x-ray excitation up to 6.5 keV photon energy demonstrate that it is possible to obtain selected-area x-ray photoemission spectra from regions less than 500 nm in diameter.
Hole scavenger redox potentials determine quantum efficiency and stability of Pt-decorated CdS nanorods for photocatalytic hydrogen generation
Authors: Berr Maximilian J. , Wagner Peter , Fischbach Stefan , Vaneski Aleksandar , Schneider Julian , Susha Andrei S. , Rogach Andrey L. , Jäckel Frank , Feldmann Jochen
Published: May 2012

We use Pt-decorated CdS nanorods for photocatalytic hydrogen generation in the presence of sacrificial hole scavengers. Both the quantum efficiency for hydrogen generation and the stability of the colloidal nanocrystals in solution improve with increasing redox potential of the hole scavenger. The higher redox potential leads to faster hole scavenging, which increases quantum efficiency and stability since electron hole recombination and oxidation of the CdS become less important. The quantum efficiencies can be tuned over more than an order of magnitude. This finding is important for choosing hole scavengers and for comparing efficiencies and stabilities for different photocatalytic nanosystems.
Ferromagnetic Josephson switching device with high characteristic voltage
Authors: Larkin Timofei I. , Bol’ginov Vitaly V. , Stolyarov Vasily S. , Ryazanov Valery V. , Vernik Igor V. , Tolpygo Sergey K. , Mukhanov Oleg A.
Published: May 2012

We develop a fast magnetic Josephson junction (MJJ)—a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient single flux quantum (SFQ) circuits. We present experimental results for superconductor-insulator-ferromagnet-superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 μV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ∼30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.
Atomistic simulations of heat transport in real-scale silicon nanowire devices
Authors: Duchemin Ivan , Donadio Davide
Published: May 2012

Utilizing atomistic lattice dynamics and scattering theory, we study thermal transport in nanodevices made of 10 nm thick silicon nanowires, from 10 to 100 nm long, sandwiched between two bulk reservoirs. We find that thermal transport in devices differs significantly from that of suspended extended nanowires, due to phonon scattering at the contact interfaces. We show that thermal conductance and the phonon transport regime can be tuned from ballistic to diffusive by varying the surface roughness of the nanowires and their length. In devices containing short crystalline wires, phonon tunneling occurs and enhances the conductance beyond that of single contacts.
Electrophoretic motion of a charged water droplet near an oil-air interface
Authors: Woog Lee Dong , Jin Im Do , Kang In Seok
Published: May 2012

The trajectory of a charged droplet near an oil-air interface is investigated. When a charged droplet is translated in oil by electrophoresis, the droplet follows a straight line between two electrodes. However, if an oil-air interface is close to a droplet, the droplet follows an upwardly concave parabolic pathway. By using the leaky dielectric model, we have verified that this phenomenon is caused by the distorted electric field due to the difference in permittivities. Furthermore, it is enhanced by the accumulated free charges on the oil-air interface due to the difference in the electric conductivities of oil and air. Finally, we suggest a complementary arrangement of electrodes for realizing a straight pathway of the droplet near the interface.
The effects of thermal stimuli on intracellular calcium change and histamine releases in rat basophilic leukemia mast cells
Authors: Wu Zu-Hui , Zhu Dan , Chen Ji-Yao , Zhou Lu-Wei
Published: May 2012

The effects of thermal stimuli on rat basophilic leukemia mast cells were studied. The cells in calcium-contained or calcium-free buffers were thermally stimulated in the temperature range of 25–60 °C. The corresponding calcium ion concentration in cells [Ca2+]i as well as the released histamine from cells was measured with fluorescence staining methods. The ruthenium red (RR), a block of membrane calcium channels (transient receptor potential family V (TRPV)), was used in experiments. Under the stimulus of 25–50 °C, no significant difference on [Ca2+]i was found between these three groups of the cells in calcium-contained buffer without or with RR and cells in calcium-free saline, indicating that the increased calcium in cytosol did not result from the extracellular buffer but came from the intracellular calcium stores. The [Ca2+]i continuously increased under the temperature of 50–60 °C, but the RR and calcium-free saline can obviously diminish the [Ca2+]i increase at these high temperatures, reflecting that the opening of the TRPV2 channels leads to a calcium influx resulting in the [Ca2+]i increment. The histamine release also became significant in these cases. Since the released histamine is a well-known mediator for the microcirculation promotion, the histamine release from mast cells could be one of the mechanisms of thermal therapy.
Off-state breakdown and dispersion optimization in AlGaN/GaN heterojunction field-effect transistors utilizing carbon doped buffer
Authors: Chevtchenko S. A. , Cho E. , Brunner F. , Bahat-Treidel E. , Würfl J.
Published: May 2012

An example of GaN buffer structure optimization in AlGaN/GaN heterojunction field-effect transistors is demonstrated. Transistors fabricated on four epitaxial structures with buffer consisting of unintentionally doped GaN channel (35 nm or 100 nm) and carbon doped GaN:C layers (∼1 × 1018 cm−3 or ∼1 × 1017 cm−3) are compared. As the criteria for optimization off-state breakdown voltage (Vbr) and drain current dispersion are used. The observed trade-off between the two parameters and dependency of Vbr on the carbon concentration and on the channel thickness are explained by a potential barrier formed due to GaN:C part of the buffer.
Enhanced optical limiting in nanosized mixed zinc ferrites
Authors: Chantharasupawong Panit , Philip Reji , Endo Tamio , Thomas Jayan
Published: May 2012

Optical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532 nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C60.
Soil acidity and exchangeable cations in remnant natural and plantation forests in the urbanised Pearl River Delta, China
Authors: Hou Enqing , Wen Dazhi , Li Jianli , Zuo Weidong , Zhang Lingling , Kuang Yuanwen , Li Jiong
Published: May 2012

Increasing urbanisation and industrialisation have led to a dramatic reduction in forest area, and now only culturally protected remnants of natural forests and some new plantations remain in most areas of the Pearl River Delta (PRD), China. To investigate the status of soil acidity and exchangeable cations under these remnant forests and assess the possible impacts of reforestation on soil nutrients in the plantation forests, soils at 0–0.03, 0.03–0.13, and 0.13–0.23 m depths were sampled from 16 forest patches (eight natural and eight plantations), and soil pH in water, organic matter content, and exchangeable cation (H, Al, Ca, Mg, K, and Na) contents were determined. Results showed that 90% of the soils were strongly acid (pH <4.5) and 70% of the soils had a base saturation <15%. About 50% of the soils had <0.5 mmol(+)/kg of exchangeable Mg. Soil exchangeable K and Mg contents were significantly lower under plantation forests than under native forests in all layers, whereas exchangeable Ca and Na contents showed little difference between two types of forests. Moreover, contents of all exchangeable cations except Al showed a significant decrease with depth. These results suggest that remnant forests in the PRD generally experience a high risk of Al and acidity stresses and non-acidic cation deficiencies for plant growth. Reforestation may cause further decline in soil exchangeable K and Mg contents, but is unlikely to affect soil exchangeable Ca and Na contents.
Seasonal variation in fire temperature and influence on soil CO2 efflux, root biomass, and soil water properties in a Sudanian savanna - woodland, West Africa
Authors: Savadogo Patrice , Santi Saïdou , Dayamba Sidzabda Djibril , Nacro Hassan Bismark , Sawadogo Louis
Published: May 2012

Savanna ecosystems are shaped mainly by fires, the consequences of which depend on both their intensities and the season in which they occur. The effects of fire disturbance on key soil parameters are still largely unknown, yet the knowledge of those effects are crucial to our understanding and management of savanna ecosystems. This study was aimed at determining seasonal variations in fire temperature and the influence of fire on soil respiration, root biomass, and soil water infiltration. It was conducted on long-term experimental plots established in 2006 in the savanna–woodland of Burkina Faso. Four fire treatments were applied: no fire, early fire, mid dry-season fire, and late dry-season fire. The results indicated that the average maximum temperature and the residence time of the lethal temperature varied significantly (P < 0.05) depending on the season of fire occurrence, the location of the soil probe, and the interaction between these two factors. The duration of heating above the critical temperature threshold was generally longest at ground level. The season in which fire occurred significantly (P ≤ 0.001) affected soil respiration, soil root biomass, and soil water infiltration. In conclusion, although fire can be used as a management tool in the savanna, the effects of fire on soil should be considered.
Transcriptional repression via antilooping in the
Drosophila
embryo
Authors: Chopra Vivek S. , Kong Nikki , Levine Michael
Published: May 2012

Transcriptional repressors are thought to inhibit gene expression by interfering with the binding or function of RNA Polymerase II, perhaps by promoting local chromatin condensation. Here, we present evidence for a distinctive mechanism of repression, whereby sequence-specific repressors prevent the looping of distal enhancers to the promoter. Particular efforts focus on the Snail repressor, which plays a conserved role in promoting epithelial-mesenchyme transitions in both invertebrates and vertebrates, including mesoderm invagination in
Drosophila
, neural crest migration in vertebrates, and tumorigenesis in mammals. Chromosome conformation capture experiments were used to examine enhancer looping at Snail target genes in wild-type and mutant embryos. These studies suggest that the Snail repressor blocks the formation of fruitful enhancer–promoter interactions when bound to a distal enhancer. This higher-order mechanism of transcriptional repression has broad implications for the control of gene activity in metazoan development.
Stress and aging induce distinct polyQ protein aggregation states
Authors: Moronetti Mazzeo Lorenza E. , Dersh Devin , Boccitto Marco , Kalb Robert G. , Lamitina Todd
Published: May 2012

Many age-related diseases are known to elicit protein misfolding and aggregation. Whereas environmental stressors, such as temperature, oxidative stress, and osmotic stress, can also damage proteins, it is not known whether aging and the environment impact protein folding in the same or different ways. Using polyQ reporters of protein folding in both
Caenorhabditis elegans
and mammalian cell culture, we show that osmotic stress, but not other proteotoxic stressors, induces rapid (minutes) cytoplasmic polyQ aggregation. Osmotic stress-induced polyQ aggregates could be distinguished from aging-induced polyQ aggregates based on morphological, biophysical, cell biological, and biochemical criteria, suggesting that they are a unique misfolded-protein species. The insulin-like growth factor signaling mutant
daf-2
, which inhibits age-induced polyQ aggregation and protects
C. elegans
from stress, did not prevent the formation of stress-induced polyQ aggregates. However, osmotic stress resistance mutants, which genetically activate the osmotic stress response, strongly inhibited the formation of osmotic polyQ aggregates. Our findings show that in vivo, the same protein can adopt distinct aggregation states depending on the initiating stressor and that stress and aging impact the proteome in related but distinct ways.
Anti-Arrhenius cleavage of covalent bonds in bottlebrush macromolecules on substrate
Authors: Lebedeva Natalia V. , Nese Alper , Sun Frank C. , Matyjaszewski Krzysztof , Sheiko Sergei S.
Published: May 2012

Spontaneous degradation of bottlebrush macromolecules on aqueous substrates was monitored by atomic force microscopy. Scission of C─C covalent bonds in the brush backbone occurred due to steric repulsion between the adsorbed side chains, which generated bond tension on the order of several nano-Newtons. Unlike conventional chemical reactions, the rate of bond scission was shown to decrease with temperature. This apparent anti-Arrhenius behavior was caused by a decrease in the surface energy of the underlying substrate upon heating, which results in a corresponding decrease of bond tension in the adsorbed macromolecules. Even though the tension dropped minimally from 2.16 to 1.89 nN, this was sufficient to overpower the increase in the thermal energy (
k
B
T
) in the Arrhenius equation. The rate constant of the bond-scission reaction was measured as a function of temperature and surface energy. Fitting the experimental data by a perturbed Morse potential
V
 = 
V
0
(1 - 
e

-
βx

)
2
 - 
fx
, we determined the depth and width of the potential to be
V
0
 = 141 ± 19 kJ/mol and
β
-1
 = 0.18 ± 0.03 
Å
, respectively. Whereas the
V
0
value is in reasonable agreement with the activation energy
E

a

 = 80–220 kJ/mol of mechanical and thermal degradation of organic polymers, it is significantly lower than the dissociation energy of a C─C bond
D

e

 = 350 kJ/mol. Moreover, the force constant
K

x

 = 2
β
2
V
0
 = 1.45 ± 0.36 kN/m of a strained bottlebrush along its backbone is markedly larger than the force constant of a C─C bond
K

l

 = 0.44 kN/m, which is attributed to additional stiffness due to deformation of the side chains.
Immediate antiviral therapy appears to restrict resting CD4
+
cell HIV-1 infection without accelerating the decay of latent infection
Authors: Archin Nancie M. , Vaidya Naveen K. , Kuruc JoAnn D. , Liberty Abigail L. , Wiegand Ann , Kearney Mary F. , Cohen Myron S. , Coffin John M. , Bosch Ronald J. , Gay Cynthia L. , Eron Joseph J. , Margolis David M. , Perelson Alan S.
Published: May 2012

HIV type 1 (HIV-1) persists within resting CD4
+
T cells despite antiretroviral therapy (ART). To better understand the kinetics by which resting cell infection (RCI) is established, we developed a mathematical model that accurately predicts (
r
= 0.65,
P
= 2.5 × 10
−4
) the initial frequency of RCI measured about 1 year postinfection, based on the time of ART initiation and the dynamic changes in viremia and CD4
+
T cells. In the largest cohort of patients treated during acute seronegative HIV infection (AHI) in whom RCI has been stringently quantified, we found that early ART reduced the generation of latently infected cells. Although RCI declined after the first year of ART in most acutely infected patients, there was a striking absence of decline when initial RCI frequency was less than 0.5 per million. Notably, low-level viremia was observed more frequently as RCI increased. Together these observations suggest that (
i
) the degree of RCI is directly related to the availability of CD4
+
T cells susceptible to HIV, whether viremia is controlled by the immune response and/or ART; and (
ii
) that two pools of infected resting CD4
+
T cells exist, namely, less stable cells, observable in patients in whom viremia is not well controlled in early infection, and extremely stable cells that are established despite early ART. These findings reinforce and extend the concept that new approaches will be needed to eradicate HIV infection, and, in particular, highlight the need to target the extremely small but universal, long-lived latent reservoir.
Cyanobacteria blooms produce teratogenic retinoic acids
Authors: Wu Xiaoqin , Jiang Jieqiong , Wan Yi , Giesy John P. , Hu Jianying
Published: May 2012

Deformed amphibians have been observed in eutrophic habitats, and some clues point to the retinoic acids (RAs) or RA mimics. However, RAs are generally thought of as vertebrate-specific hormones, and there was no evidence that RAs exist in cyanobacteria or algae blooms. By analyzing RAs and their analogs 4-oxo-RAs in natural cyanobacteria blooms and cultures of cyanobacteria and algae, we showed that cyanobacteria blooms could produce RAs, which were powerful animal teratogens. Intracellular RAs and 4-oxo-RAs with concentrations between 0.4 and 4.2 × 10
2
ng/L were detected in all bloom materials, and extracellular concentrations measured in water from Taihu Lake, China, were as great as 2.0 × 10 ng/L, which might pose a risk to wildlife through chronic exposure. Further examination of 39 cyanobacteria and algae species revealed that 32 species could produce RAs and 4-oxo-RAs (1.6–1.4 × 10
3
ng/g dry weight), and the dominant cyanobacteria species in Taihu Lake,
Microcystis flos-aquae
and
Microcystis aeruginosa
, produced high amounts of RAs and 4-oxo-RAs with concentrations of 1.4 × 10
3
and 3.7 × 10
2
ng/g dry weight, respectively. Most genera of cyanobacteria that could produce RAs and 4-oxo-RAs, such as
Microcystis
,
Anabaena
, and
Aphanizomenon
, often occur dominantly in blooms. Production of RAs and 4-oxo-RAs by cyanobacteria was associated with species, origin location, and growth stage. These results represent a conclusive demonstration of endogenous production of RAs in freshwater cyanobacteria blooms. The observation of teratogenic RAs in cyanobacteria is evolutionarily and ecologically significant because RAs are vertebrate-specific hormones, and cyanobacteria form extensive and highly visible blooms in many aquatic ecosystems.
Robust cardiomyocyte differentiation from human pluripotent stem cells via temporal modulation of canonical Wnt signaling
Authors: Lian Xiaojun , Hsiao Cheston , Wilson Gisela , Zhu Kexian , Hazeltine Laurie B. , Azarin Samira M. , Raval Kunil K. , Zhang Jianhua , Kamp Timothy J. , Palecek Sean P.
Published: May 2012

Human pluripotent stem cells (hPSCs) offer the potential to generate large numbers of functional cardiomyocytes from clonal and patient-specific cell sources. Here we show that temporal modulation of Wnt signaling is both essential and sufficient for efficient cardiac induction in hPSCs under defined, growth factor-free conditions. shRNA knockdown of β-catenin during the initial stage of hPSC differentiation fully blocked cardiomyocyte specification, whereas glycogen synthase kinase 3 inhibition at this point enhanced cardiomyocyte generation. Furthermore, sequential treatment of hPSCs with glycogen synthase kinase 3 inhibitors followed by inducible expression of β-catenin shRNA or chemical inhibitors of Wnt signaling produced a high yield of virtually (up to 98%) pure functional human cardiomyocytes from multiple hPSC lines. The robust ability to generate functional cardiomyocytes under defined, growth factor-free conditions solely by genetic or chemically mediated manipulation of a single developmental pathway should facilitate scalable production of cardiac cells suitable for research and regenerative applications.
Human origins and the transition from promiscuity to pair-bonding
Authors: Gavrilets Sergey
Published: May 2012

A crucial step in recent theories of human origins is the emergence of strong pair-bonding between males and females accompanied by a dramatic reduction in the male-to-male conflict over mating and an increased investment in offspring. How such a transition from promiscuity to pair-bonding could be achieved is puzzling. Many species would, indeed, be much better off evolutionarily if the effort spent on male competition over mating was redirected to increasing female fertility or survivorship of offspring. Males, however, are locked in a “social dilemma,” where shifting one’s effort from “appropriation” to “production” would give an advantage to free-riding competitors and therefore, should not happen. Here, I first consider simple models for four prominent scenarios of the human transition to pair-bonding: communal care, mate guarding, food for mating, and mate provisioning. I show that the transition is not feasible under biologically relevant conditions in any of these models. Then, I show that the transition can happen if one accounts for male heterogeneity, assortative pair formation, and evolution of female choice and faithfulness. This process is started when low-ranked males begin using an alternative strategy of female provisioning. At the end, except for the top-ranked individuals, males invest exclusively in provisioning females who have evolved very high fidelity to their mates. My results point to the crucial importance of female choice and emphasize the need for incorporating between-individual variation in theoretical and empirical studies of social dilemmas and behaviors.
Identification of an abscisic acid transporter by functional screening using the receptor complex as a sensor
Authors: Kanno Yuri , Hanada Atsushi , Chiba Yasutaka , Ichikawa Takanari , Nakazawa Miki , Matsui Minami , Koshiba Tomokazu , Kamiya Yuji , Seo Mitsunori
Published: May 2012

Movement of the plant hormone abscisic acid (ABA) within plants has been documented; however, the molecular mechanisms that regulate ABA transport are not fully understood. By using a modified yeast two-hybrid system, we screened
Arabidopsis
cDNAs capable of inducing interactions between the ABA receptor PYR/PYL/RCAR and PP2C protein phosphatase under low ABA concentrations. By using this approach, we identified four members of the NRT1/PTR family as candidates for ABA importers. Transport assays in yeast and insect cells demonstrated that at least one of the candidates ABA-IMPORTING TRANSPORTER (AIT) 1, which had been characterized as the low-affinity nitrate transporter NRT1.2, mediates cellular ABA uptake. Compared with WT, the
ait1
/
nrt1
.
2
mutants were less sensitive to exogenously applied ABA during seed germination and/or postgermination growth, whereas overexpression of
AIT1
/
NRT1
.
2
resulted in ABA hypersensitivity in the same conditions. Interestingly, the inflorescence stems of
ait1
/
nrt1
.
2
had a lower surface temperature than those of the WT because of excess water loss from open stomata. We detected promoter activities of
AIT1
/
NRT1
.
2
around vascular tissues in inflorescence stems, leaves, and roots. These data suggest that the function of
AIT1
/
NRT1
.
2
as an ABA importer at the site of ABA biosynthesis is important for the regulation of stomatal aperture in inflorescence stems.
3′ Phosphatase activity toward phosphatidylinositol 3,4-bisphosphate [PI(3,4)P
2
] by voltage-sensing phosphatase (VSP)
Authors: Kurokawa Tatsuki , Takasuga Shunsuke , Sakata Souhei , Yamaguchi Shinji , Horie Shigeo , Homma Koichi J. , Sasaki Takehiko , Okamura Yasushi
Published: May 2012

Voltage-sensing phosphatases (VSPs) consist of a voltage-sensor domain and a cytoplasmic region with remarkable sequence similarity to phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor phosphatase. VSPs dephosphorylate the 5′ position of the inositol ring of both phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P
3
] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P
2
] upon voltage depolarization. However, it is unclear whether VSPs also have 3′ phosphatase activity. To gain insights into this question, we performed in vitro assays of phosphatase activities of
Ciona intestinalis
VSP (Ci-VSP) and transmembrane phosphatase with tensin homology (TPTE) and PTEN homologous inositol lipid phosphatase (TPIP; one human ortholog of VSP) with radiolabeled PI(3,4,5)P
3
. TLC assay showed that the 3′ phosphate of PI(3,4,5)P
3
was not dephosphorylated, whereas that of phosphatidylinositol 3,4-bisphosphate [PI(3,4)P
2
] was removed by VSPs. Monitoring of PI(3,4)P
2
levels with the pleckstrin homology (PH) domain from tandem PH domain-containing protein (TAPP1) fused with GFP (PH
TAPP1
-GFP) by confocal microscopy in amphibian oocytes showed an increase of fluorescence intensity during depolarization to 0 mV, consistent with 5′ phosphatase activity of VSP toward PI(3,4,5)P
3
. However, depolarization to 60 mV showed a transient increase of GFP fluorescence followed by a decrease, indicating that, after PI(3,4,5)P
3
is dephosphorylated at the 5′ position, PI(3,4)P
2
is then dephosphorylated at the 3′ position. These results suggest that substrate specificity of the VSP changes with membrane potential.