bluuebunny/crossref_metadata_2025 huggingface dataset:
An investigation of the influence of cell topography on epithelial mechanical stresses during pulmonary airway reopening
Authors: Jacob A. M. , Gaver D. P.
Published: February 2005

The goal of this study is to assess the local mechanical environment of the pulmonary epithelium in a computational model of airway reopening. To this end, the boundary element method (BEM) in conjunction with lubrication theory is implemented to assess the stationary-state behavior of a semi-infinite bubble traveling through a liquid-occluded parallel plate flow chamber lined with epithelial cells. The fluid occlusion is assumed to be Newtonian and inertia is neglected. The interactions between the microgeometry of the model airway’s walls and the interfacial kinematics surrounding the bubble’s tip result in a complex, spatially and temporally dependent stress distribution. The walls’ nonplanar topography magnifies the normal and shear stresses and stress gradients. We find that decreasing the bubble’s speed serves to increase the maximum normal stress and stress gradient but decrease the maximum shear stress and stress gradient. Our results give credence to the pressure-gradient-induced epithelial damage theory recently proposed by Bilek et al. [J. Appl. Physiol. 94, 770 (2003)] and Kay et al. [J. Appl. Physiol. 97, 269 (2004)]. We conclude that the amplified pressure gradients found in this study may be even more detrimental to the airway’s cellular epithelium during airway reopening.
A vortex model for Richtmyer–Meshkov instability accounting for finite Atwood number
Authors: Likhachev Oleg A. , Jacobs Jeffrey W.
Published: February 2005

The vortex model developed by Jacobs and Sheeley [“Experimental study of incompressible Richtmyer–Meshkov instability,” Phys. Fluids 8, 405 (1996)] is essentially a solution to the governing equations for the case of a uniform density fluid. Thus, this model strictly speaking only applies to the case of vanishing small Atwood number. A modification to this model for small to finite Atwood number is proposed in which the vortex row utilized is perturbed such that the vortex spacing is smaller across the spikes and larger across the bubbles, a fact readily observed in experimental images. It is shown that this modification more effectively captures the behavior of experimental amplitude measurements, especially when compared with separate bubble and spike data. In addition, it is shown that this modification will cause the amplitude to deviate from the logarithmic result given by the heuristic models at late time.
Large plasma-edge broadened magneto-optic-polar-Kerr-effect-based broadband incoherent detection of terahertz spectral frequencies
Authors: De A. , Puri A.
Published: February 2005

A magneto-optic Kerr effect (MOKE)-based spectroscopic technique is proposed in the terahertz regime. This method relies on very large reflection edge splitting effects, which occur when the cyclotron frequency (CF) is of the same order of magnitude or greater than the plasma frequency. In the event of a very large reflection edge split, the Kerr rotation (KR) no longer occurs at the plasma edge, but instead occurs at Re(ε+ε−)≈1, within the macroscopic framework of the Drude model. This implies that one can control the spectral occurrence of the MOKE resonance, simply by tuning the magnetic field strength. This phenomenon is unheard of for much shorter wavelengths, due to practical limitations on required magnetic field strengths and hence, can only be realized in the THz regime. A 3 T magnet can easily cover the proposed 0.5–5 THz spectral range for an InSb substrate. Our calculations show that in order to achieve good spectral resolution, the InSb substrate needs to be cooled to 77 K. The Kerr rotation obtained at 77 K for a CF of 1 THz is about 6.28°, which can be increased to about 18.35° by coating a thin low refractive index material on the InSb substrate. A well established ellipsometric technique, which uses four incoherent detectors, is proposed, for fast-simultaneous measurement of KR, Kerr ellipticity and reflectivity.
Effective pyroelectric response of compositionally graded ferroelectric materials
Authors: Zhong S. , Alpay S. P. , Ban Z.-G. , Mantese J. V.
Published: February 2005

A thermodynamic theory is used to determine the effective pyroelectric coefficients of polarization graded ferroelectrics, with values in excess of 0.1μC∕cm2°C are predicted for various barium strontium titanate thin films. Maximum values closer to 0.4μC∕cm2°C are obtained for a 1μm thick material—compositionally graded between pure barium titanate and one that has barium to strontium in the ratio of 75:25.
Flexible organic photovoltaics using conducting polymer electrodes
Authors: Kushto Gary P. , Kim Woohong , Kafafi Zakya H.
Published: February 2005

Single heterojunction, small-molecule organic photovoltaic devices (OPVs) have been prepared on fully flexible thermoplastic substrates using prepatterned conducting polymer electrodes(∼450Ω∕◻). OPVs were fabricated via sequential vacuum vapor deposition of layers of the organic electron donating/hole transporting material: N,N′-(α-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine and the electron accepting/transporting material: C60. The resulting photovoltaic cells exhibit white-light power conversion efficiencies of 1% (AM1.5, 97mW∕cm2), virtually identical to those fabricated on prepatterned tin-doped indium oxide/glass substrates.
Numerical modeling of the induced grating autocorrelation for studying optical fiber nonlinearities in the picosecond regime
Authors: Oguama F. A. , Tchouassi A. , Johnson A. M. , Garcia Hernando
Published: February 2005

We report a direct numerical model of the induced grating autocorrelation (IGA) based on the numerical solution of the nonlinear Schrödinger equation for an intense optical pulse that has experienced nonlinear distortion [notably, self-phase modulation (SPM) and stimulated Raman scattering (SRS)] after propagating through an optical fiber. Our numerical simulations are in good agreement with experiments. A significant advantage of the numerical approach over the well-known analytical models is its capability to predict IGA traces in the presence of pump depletion. In the light of this, IGA can now be used to study the combined effects of SPM and SRS in optical fibers in the regime where pump depletion is important, and both the nonlinear refractive index and the Raman gain coefficient of the fiber can be extracted.
Performance improvement of polycrystalline diamond ultraviolet photodetectors by room-temperature plasma treatment
Authors: Wang S. G. , Sellin P. J. , Lohstroh A. , Zhang Qing
Published: February 2005

Enhancement of ultraviolet (UV) photoresponsivity in chemical-vapor-deposited (CVD) diamond photodetectors was observed by posttreatment in a plasma of oxygen and carbon tetrafluoride at room temperature. This room-temperature plasma posttreatment was found to be an efficient process in suppressing the extrinsic photoresponse of CVD diamond UV photodetectors in the visible region. Nearly four orders of magnitude difference in the photoresponsivity between the UV and visible light regions were obtained. The results of photoluminescence mapping and Raman spectra indicate that this performance improvement may have resulted from the effective removal of the sp2-bonded carbon impurities and passivation of the silicon-vacancy defects in the diamond.
Spectroscopic characterization of 1.3μm GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy
Authors: Sun H. D. , Clark A. H. , Calvez S. , Dawson M. D. , Qiu Y. N. , Rorison J. M. , Kim K. S. , Kim T. , Park Y. J.
Published: February 2005

We report optical studies of high-quality 1.3μm strain-compensated GaInNAs∕GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum.
Improvement in performance of transparent organic light-emitting diodes with increasing sputtering power in the deposition of indium tin oxide cathode
Authors: Chung Choong-Heui , Ko Young-Wook , Kim Yong-Hae , Sohn Choong-Yong , Chu Hye Yong , Lee Jin Ho
Published: February 2005

The performance of transparent organic light-emitting diodes (OLEDs) can be substantially improved by increasing the rf sputtering power in the deposition of an indium tin oxide cathode. This dependence of device performance on sputtering power is quite different from that reported for transparent OLEDs. The effect is attributed to sputtering induced substrate-heating resulting in chemical reactions at the Al–LiF–Alq3 interface and electron injection enhancement. By effectively dissipating the energy of sputtered particles, device damage can be taken away. The findings herein show that a transparent OLED having better electron injection properties than a conventional OLED can be fabricated.
Interaction of atomic hydrogen with Zn-polar and O-polar ZnO surfaces
Authors: Losurdo Maria , Giangregorio Maria M.
Published: February 2005

The interaction of Zn-polar and O-polar ZnO surfaces with atomic hydrogen produced by a remote rf plasma source is investigated in situ and in real time using spectroscopic ellipsometry. It is found that the reactivity of ZnO with atomic hydrogen depends on polarity. The interaction of O-polar surfaces with atomic hydrogen at 100 °C is suitable for producing clean surfaces, while Zn-polar surfaces strongly react with atomic hydrogen resulting in a disruption of the ZnO lattice with formation of Zn surface clusters.
Suspended single-electron transistors: Fabrication and measurement
Authors: Paraoanu G. S. , Halvari A. M.
Published: February 2005

We have fabricated suspended aluminum single-electron transistors in which the island is not in contact with the substrate. This type of device displays well-defined I-V and dI∕dV-V features typical for high-quality standard superconducting single-electron transistors.
Near- and mid-infrared detection using GaAs∕InxGa1−xAs∕InyGa1−yAs multiple step quantum wells
Authors: Touse M. P. , Karunasiri G. , Lantz K. R. , Li H. , Mei T.
Published: February 2005

A dual-band multiple-quantum-well infrared photodetector capable of simultaneously detecting wavelengths near 0.9 μm and 10 μm has been fabricated using GaAs∕InGaAs step quantum wells. The detection of the near (0.82–0.95 μm)- and mid (9–11 μm)-infrared wavelength bands was achieved using interband and intersubband transitions. The measured peak responsivities of the near- and mid-infrared bands were 0.4 A∕W and 1 A∕W, respectively, at 0.8 V bias across the device. The broken symmetry of the step quantum well allows transitions from the ground states of heavy and light holes to the first-excited electron state allowing the photoexcited carriers to be efficiently collected. The estimated values of the detectivities for near- and mid-infrared bands at 40 K and 0.8 V bias are approximately 4.5×109cm(Hz)1∕2∕W and 1.1×1010cm(Hz)1∕2∕W, respectively.
Lattice strain analysis of transistor structures with silicon–germanium and silicon–carbon source∕drain stressors
Authors: Ang Kah-Wee , Chui King-Jien , Bliznetsov Vladimir , Tung Chih-Hang , Du Anyan , Balasubramanian Narayanan , Samudra Ganesh , Li Ming Fu , Yeo Yee-Chia
Published: February 2005

We report the characterization of strain components in transistor structures with silicon–germanium (Si0.75Ge0.25) and silicon–carbon (Si0.99C0.01) stressors grown by selective epitaxy in the source and drain regions. The spacing between the source and drain stressors is 35nm. Lattice strain analysis was performed using high-resolution transmission electron microscopy (HRTEM) and diffractograms obtained by fast Fourier transform of HRTEM images. The lateral strain component εxx and the vertical strain component εzz were derived from the (220) and (002) reflections in the diffractogram, respectively. SiGe source and drain stressors lead to lateral compressive strain and vertical tensile strain in the Si channel. On the other hand, the SiC source and drain stressors give rise to lateral tensile strain and vertical compressive strain in the Si channel, an effect complementary to that of SiGe source∕drain stressors. The results of this work will be useful for channel strain engineering in complementary metal-oxide-semiconductor transistors.
Photoinduced generation of electron anions in H-doped nanoporous oxide 12CaO∙7Al2O3: Toward an optically controlled formation of electrides
Authors: Sushko Peter V. , Shluger Alexander L. , Hayashi Katsuro , Hirano Masahiro , Hosono Hideo
Published: February 2005

We suggest, on the basis of detailed ab initio calculations of both ground and photoexcited states of H-doped 12CaO∙7Al2O3 (C12A7:H), that stable high-conductivity regions can be optically generated in this insulating system. Each H− ion in C12A7:H can, under photoirradiation at 3.8–4.5 eV, produce up to two electrons and a proton that binds to the lattice network and forms OH−. Mobile electrons play a role of anions in this system. They move over subnanosized cages of the C12A7 lattice via polaron hopping. The insulating state is reversibly restored upon heating to 300 °C.
Magnetocapacitance probing of the many-particle states in InAs dots
Authors: Wibbelhoff Oliver S. , Lorke Axel , Reuter Dirk , Wieck Andreas D.
Published: February 2005

We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasiparticle wave functions in momentum space for one to two electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high-energy orbitals exhibit signatures of anisotropic confinement and correlation effects.
Add-drop filters utilizing vertically coupled microdisk resonators in silicon
Authors: Koonath Prakash , Indukuri Tejaswi , Jalali Bahram
Published: February 2005

Add-drop filters, based on vertically coupled microdisk resonators, have been realized in silicon, using a modified separation by implantation of oxygen process. Buried rib waveguides in the bottom-layer silicon, of a two-layer structure, are coupled to microdisk resonators in the top-layer silicon through a silicon dioxide layer formed by oxygen implantation. The radii of the microdisk structures were varied suitably to obtain resonators with slightly shifted resonance wavelengths. The average adjacent channel crosstalk suppression of these filters exhibits an upper limit of 12.11dB and a lower limit of 6.2dB over the wavelength band under consideration.
Statistical mechanics characterization of neuronal mosaics
Authors: da Fontoura Costa Luciano , Rocha Fernando , Araújo de Lima Silene Maria
Published: February 2005

The spatial distribution of neuronal cells is an important requirement for achieving proper neuronal function in several parts of the nervous system of most animals. For instance, specific distribution of photoreceptors and related neuronal cells, particularly the ganglion cells, in a mammal’s retina is required in order to properly sample the projected scene. This work presents how two concepts from the areas of statistical mechanics and complex systems, namely the lacunarity and the multiscale entropy (i.e., the entropy calculated over progressively diffused representations of the cell mosaic), have allowed effective characterization of the spatial distribution of retinal cells.
Creating Lean Industrial Relations: General Motors in Silao, Mexico
Authors: Rothstein Jeffrey S.
Published: February 2005

Research demonstrates that firms tailor their ‘lean production’ systems to take advantage of local cultural, industrial and labour relations environments to enhance productivity and at specific worksites. This article analyses the human resource policies practised by General Motors (GM) and their suppliers in Silao, Mexico to identify two local innovations to the automaker's lean production system. First, GM achieved the labour stability necessary to implement lean production by meticulously selecting workers and by embracing a local labour union eager to work with the firm. Secondly, GM and its local suppliers co-ordinated a single industrial relations regime, dividing the local labour force between them and maintaining a pay hierarchy among the plants. Doing so increased their collective efficiency by matching each of the factory's production processes with a capable segment of the labour market while stifling wage inflation by reducing competition among them.
Software Export Success Factors and Strategies in ‘Follower’ Nations
Authors: Heeks Richard , Nicholson Brian
Published: February 2005

Many countries world-wide are becoming active or interested in software exports. This paper initially analyses the software export experiences of India, Ireland and Israel; the three largest software ‘followers’ (those which developed a software industry after the 1970s). It develops a new ‘Software Export Success Model’ on the basis of that analysis. This model, having been developed as a descriptive/analytical framework, is then applied in a number of ways. First, as a comparative framework, helping to identify current strengths and weaknesses of two ‘second-tier’ followers – Russia and China – as compared particularly with India. Secondly, as a predictive foundation for understanding likely sectoral trajectories within these second-tier nations. Finally, as a prescriptive foundation from which guidance can be derived on the strategies and interventions that these countries may need to adopt for software export growth. As well as demonstrating the value of this new framework for conceptual analysis, this paper also shows how it can have practical value to policy-makers, industry association representatives, consultants and others involved with software sector strategy. Although beyond the scope of this paper, it appears that the model will also serve as a framework for equivalent analysis and guidance for the many other follower nations who have recently entered into software exports.
Perspectives on lifestyle intervention: The views of general practitioners who have taken part in a health promotion study
Authors: Jacobsen Eva T. , Rasmussen Susanne R. , Christensen Majbritt , Engberg Marianne , Lauritzen Torsten
Published: February 2005

Aim: A study was carried out to discover the views of Danish general practitioners on the possibility of intervening in their patients' lifestyles in general and on the obstacles to doing so, based on their experience of participating in a health promotion study. Method: A focus group interview was conducted with five general practitioners who had participated in ``The Ebeltoft Health Promotion Study'' to assess their views on their preventive role. Results: The general practitioners have internalized the view advanced by society and the medical profession that they have an important role to play in preventing lifestyle-related illness. However, they are sceptical about the effectiveness of intervention and have ethical concerns about giving lifestyle advice. They are also somewhat irritated by the fact that patients are chiefly interested in having their health checked, rather than in following up by changing their behaviour. The general practitioners differ in their views as to when, and how actively, they should initiate discussions with individual patients to encourage them to change their lifestyles. Conclusions: If the medical profession and those responsible for overall health policy wish to make general practitioners change their behaviour towards their patients, it is important that they understand the aims, values, and working conditions of general practitioners that underlie their present attitudes and behaviour.
Pharmaceutical insurance and the demand for prescription pharmaceuticals in Västerbotten, Sweden
Authors: Rudholm Niklas
Published: February 2005

Aims: The aim of this paper is to analyze the impact of pharmaceutical insurance on the demand for prescription pharmaceuticals in the county of Västerbotten, Sweden. As the patients do not bear the full marginal costs of the pharmaceuticals they consume when pharmaceutical insurance systems are present, this could induce patients to over-consume pharmaceutical treatments. Methods: Data covering all prescription pharmaceuticals sold in the county of Västerbotten, Sweden during the year 2001 have been provided by the local county council. Data include information concerning the gender and age of the patient, the number of defined daily doses, total cost, and the patient's co-payment for the prescription. The hypothesis that patients will consume more (or perhaps more expensive) pharmaceuticals when there is pharmaceutical insurance is tested by means of regression analysis. Results: The results show that both the quantities dispensed and the price of the pharmaceuticals consumed increase when the pharmaceutical insurance system pays part of the total cost of the pharmaceuticals consumed. Conclusions: The findings suggest that introducing a small patient co-payment for all prescriptions should be an effective measure to decrease pharmaceutical consumption.
Effects on sick leave of an inpatient rehabilitation programme for asthmatics in a randomized trial
Authors: Nathell Lennart
Published: February 2005

Aim: Among adult asthmatics a major proportion of the cost of illness is attributed to productivity losses and societal costs in connection with sick leave compensation. The aim of the study was to evaluate an extensive structured four-week inpatient rehabilitation programme for asthmatics. Methods: A diagnosis of asthma was made in a structured way among people on sick leave due to a respiratory disorder. In total, 197 persons were randomized to either a rehabilitation programme, or to usual care. The main components of the rehabilitation programme were education, pharmacological optimization, physical training, and coping skill acquisition. Results: At the three-year follow-up, the median number of sick leave days in the rehabilitation group was 104, and in the usual care group 167 (p=0.12). An analysis of a subgroup consisting of persons not currently smoking with a previous diagnosis of asthma by a physician (n=57) showed a significant effect on sick leave at three years (median number of days 63 in the rehabilitation group vs 361 in the control group, p=0.02). All analyses were based on intention to treat. Conclusions: The long-term effects on sick leave of an extensive inpatient asthma rehabilitation programme are most evident for non-smokers and ex-smokers with a previous asthma diagnosis. It is therefore recommended that persons with asthma who are current smokers should be offered participation in smoking cessation programmes instead of asthma rehabilitation programmes.
Pollen-associated phytoprostanes inhibit dendritic cell interleukin-12 production and augment T helper type 2 cell polarization
Authors: Traidl-Hoffmann Claudia , Mariani Valentina , Hochrein Hubertus , Karg Kathrin , Wagner Hermann , Ring Johannes , Mueller Martin J. , Jakob Thilo , Behrendt Heidrun
Published: February 2005

Pollen grains induce allergies in susceptible individuals by release of allergens upon contact with mucosal membranes of the upper respiratory tract. We recently demonstrated that pollen not only function as allergen carriers but also as rich sources of bioactive lipids that attract cells involved in allergic inflammation such as neutrophils and eosinophils. Here we demonstrate that soluble factors from birch (Betula alba L.) pollen activate human dendritic cells (DCs) as documented by phenotypical and functional maturation and altered cytokine production. Betula alba L. aqueous pollen extracts (Bet.-APE) selectively inhibited interleukin (IL)-12 p70 production of lipopolysaccharide (LPS)- or CD40L-activated DC, whereas IL-6, IL-10, and TNFα remained unchanged. Presence of Bet.-APE during DC activation resulted in DC with increased T helper type 2 (Th2) cell and reduced Th1 cell polarizing capacity. Chemical analysis of Bet.-APE revealed the presence of phytoprostanes (dinor isoprostanes) with prostaglandin E1-, F1-, A1-, or B1-ring systems of which only E1-phytoprostanes dose dependently inhibited the LPS-induced IL-12 p70 release and augmented the Th2 cell polarizing capacity of DC. These results suggest that pollen-derived E1-phytoprostanes not only resemble endogenous prostaglandin E2 structurally but also functionally in that they act as regulators that modulate human DC function in a fashion that favors Th2 cell polarization.
Enhanced autoantigen expression in regenerating muscle cells in idiopathic inflammatory myopathy
Authors: Casciola-Rosen Livia , Nagaraju Kanneboyina , Plotz Paul , Wang Kondi , Levine Stuart , Gabrielson Edward , Corse Andrea , Rosen Antony
Published: February 2005

Unique autoantibody specificities are strongly associated with distinct clinical phenotypes, making autoantibodies useful for diagnosis and prognosis. To investigate the mechanisms underlying this striking association, we examined autoantigen expression in normal muscle and in muscle from patients with autoimmune myositis. Although myositis autoantigens are expressed at very low levels in control muscle, they are found at high levels in myositis muscle. Furthermore, increased autoantigen expression correlates with differentiation state, such that myositis autoantigen expression is increased in cells that have features of regenerating muscle cells. Consistent with this, we found that cultured myoblasts express high levels of autoantigens, which are strikingly down-regulated as cells differentiate into myotubes in vitro. These data strongly implicate regenerating muscle cells rather than mature myotubes as the source of ongoing antigen supply in autoimmune myositis. Myositis autoantigen expression is also markedly increased in several cancers known to be associated with autoimmune myositis, but not in their related normal tissues, demonstrating that tumor cells and undifferentiated myoblasts are antigenically similar. We propose that in cancer-associated myositis, an autoimmune response directed against cancer cross-reacts with regenerating muscle cells, enabling a feed-forward loop of tissue damage and antigen selection. Regulating pathways of antigen expression may provide unrecognized therapeutic opportunities in autoimmune diseases.
Clearance of apoptotic neurons without inflammation by microglial triggering receptor expressed on myeloid cells-2
Authors: Takahashi Kazuya , Rochford Christian D.P. , Neumann Harald
Published: February 2005

Elimination of apoptotic neurons without inflammation is crucial for brain tissue homeostasis, but the molecular mechanism has not been firmly established. Triggering receptor expressed on myeloid cells-2 (TREM2) is a recently identified innate immune receptor. Here, we show expression of TREM2 in microglia. TREM2 stimulation induced DAP12 phosphorylation, extracellular signal–regulated kinase phosphorylation, and cytoskeleton reorganization and increased phagocytosis. Knockdown of TREM2 in microglia inhibited phagocytosis of apoptotic neurons and increased gene transcription of tumor necrosis factor α and nitric oxide synthase-2, whereas overexpression of TREM2 increased phagocytosis and decreased microglial proinflammatory responses. Thus, TREM2 deficiency results in impaired clearance of apoptotic neurons and inflammation that might be responsible for the brain degeneration observed in patients with polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy/Nasu-Hakola disease.
The BCL2A1 gene as a pre–T cell receptor–induced regulator of thymocyte survival
Authors: Mandal Malay , Borowski Christine , Palomero Teresa , Ferrando Adolfo A. , Oberdoerffer Philipp , Meng Fanyong , Ruiz-Vela Antonio , Ciofani Maria , Zuniga-Pflucker Juan-Carlos , Screpanti Isabella , Look A. Thomas , Korsmeyer Stanley J. , Rajewsky Klaus , von Boehmer Harald , Aifantis Iannis
Published: February 2005

The pre–T cell receptor (TCR) is expressed early during T cell development and imposes a tight selection for differentiating T cell progenitors. Pre-TCR–expressing cells are selected to survive and differentiate further, whereas pre-TCR− cells are “negatively” selected to die. The mechanisms of pre-TCR–mediated survival are poorly understood. Here, we describe the induction of the antiapoptotic gene BCL2A1 (A1) as a potential mechanism regulating inhibition of pre–T cell death. We characterize in detail the signaling pathway involved in A1 induction and show that A1 expression can induce pre–T cell survival by inhibiting activation of caspase-3. Moreover, we show that in vitro “knockdown” of A1 expression can compromise survival even in the presence of a functional pre-TCR. Finally, we suggest that pre-TCR–induced A1 overexpression can contribute to T cell leukemia in both mice and humans.
Movies, measurement, and modeling
Authors: Witt Colleen , Raychaudhuri Subhadip , Chakraborty Arup K.
Published: February 2005

Immunological phenomena that were once deduced from genetic, biochemical, and in situ approaches are now being witnessed in living color, in three dimensions, and in real time. The information in time-lapse imaging can provide valuable mechanistic insight into a host of processes, from cell migration to signal transduction. What we need now are methods to quantitate these new visual data and to exploit computational resources and statistical mechanical methods to develop mechanistic models.
On imaging, speed, and the future of lymphocyte signaling
Authors: Tarakhovsky Alexander
Published: February 2005

During a recent roundtable discussion, we captured some personal perspectives on the new insight that advanced imaging techniques promise to bring to the study of lymphocyte signaling. The experts present their views on the power of imaging, the problems that need to be overcome, and the potential of the technology.
Ascent exhalations of Antarctic fur seals: a behavioural adaptation for breath–hold diving?
Authors: Hooker Sascha K. , Miller Patrick J. O. , Johnson Mark P. , Cox Oliver P. , Boyd Ian L.
Published: February 2005

Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50–85% of ascent from all dives (10–160 m,n> 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow–water blackout.
Selective gopher disturbance influences plant species effects on nitrogen cycling
Authors: Eviner Valerie T. , Chapin, III F. Stuart
Published: February 2005

Plant species effects on ecosystem processes are mediated by traits such as litter quality and exudation. These same traits also influence the activity and distribution of animals that play key roles in regulating ecosystem dynamics. We planted monocultures of eight plant species commonly found in California grasslands to investigate the relative importance of plant species direct effects on nitrogen cycling, versus their indirect effects mediated by plant interactions with gophers. Plant species differed in their litter C:N ratio, which closely related to species effects on rates of net mineralization and nitrification in undisturbed soil. However, the effect of selective gopher disturbance on N cycling greatly altered these species effects.

Plant species differed in their effects on the type and timing of gopher disturbance. Small feeding holes were formed in late spring in plots containing species with high tissue quality. These feeding holes minimally disturbed the soil and did not alter N cycling rates over the short term. Large gopher mounds were formed in the winter and early spring, primarily in plots containing the grass,Aegilops triuncialis, and to a lesser extent in plots containingAvena barbata. These large mounds significantly disturbed the soil and greatly increased net nitrification rates, but had no consistent effects on net N mineralization. In undisturbed soil,Aegilopshad the highest litter C:N ratio and one of the lowest rates of net nitrification. However, gophers preferentially built large mounds inAegilopsplots. Once the effects of gopher burrowing were considered,Aegilopshad one of the highest rates of net nitrification, indicating that the indirect effects of plant species on N cycling can be more important than the direct effects alone. This experiment indicates that it is vital to consider interactions between plants and other organisms in order to predict the ecosystem effects of plant communities.
Is arthropod predation exclusively satiation‐driven?
Authors: Rijn Paul C. J. van , Bakker Frank M. , Hoeven Wietske A. D. van der , Sabelis Maurice W.
Published: February 2005

Functional response models differ in which factors limit predation (e.g. searching efficiency, prey handling time, digestion) and whether predation behaviour is governed by an internal physiological state (e.g. satiation). There is now much evidence that satiation is a key factor in understanding changes in foraging behaviour, and that many predators are effectively digestion limited. Here, we ask if predation in a predatory arthropod can be explained from satiation‐driven behaviour alone, or if behaviour is also influenced by the density of prey other than via the effect of prey ingestion on satiation. To address this question a satiation‐based predation model is formulated, for which parameters are estimated on the basis of observations on digestion rate, satiation‐related prey searching rate and prey capture behaviour, basically under high prey density conditions. The model predictions are subsequently tested against longer term predation experiments carried out at high and low prey densities. Since satiation can easily be linked with egg production, these tests are carried out both for predation and oviposition.

The predator–prey systems under study consist of females of two predatory mite species (Neoseiulus barkeri and N. cucumeris) and the larvae of two thrips species (Thrips tabaci and Frankliniella occidentalis) as their prey. For N. barkeri foraging on T. tabaci, the model gives good predictions at both high (4 larvae cm−1) and low (0.1–1 larvae cm−2) prey densities. For N. cucumeris foraging on F. occidentalis, the predictions hold at the high prey density, but are too low at low prey densities. Thus our analysis indicates that we cannot fully explain density‐dependent predation rates from satiation‐driven behaviour alone. Different mechanisms are suggested on how prey density may affect foraging efficiency other than via satiation.
Leaf mineral nutrition of Arctic plants in response to warming and deeper snow in northern Alaska
Authors: Welker J. M. , Fahnestock J. T. , Sullivan P. F. , Chimner R. A.
Published: February 2005

Articulating the consequences of global climate change on terrestrial ecosystem biogeochemistry is a critical component of Arctic system studies. Leaf mineral nutrition responses of tundra plants is an important measure of changes in organismic and ecosystem attributes because leaf nitrogen and carbon contents effect photosynthesis, primary production, carbon budgets, leaf litter, and soil organic matter decomposition as well as herbivore forage quality. In this study, we used a longterm experiment where snow depth and summer temperatures were increased independently and together to articulate how a series of climate change scenarios would affect leaf N, leaf C, and leaf C:N for vegetation in dry and moist tussock tundra in northern Alaska, USA. Our findings were: 1) moist tundra vegetation is much more responsive to this suite of climate change scenarios than dry tundra with up to a 25% increase in leaf N; 2) life forms exhibit divergence in leaf C, N, and C:N with deciduous shrubs and graminoids having almost identical leaf N contents; 3) for some species, leaf mineral nutrition responses to these climate change scenarios are tundra type dependent (Betula), but for others (Vaccinium vitis‐idaea), strong responses are exhibited regardless of tundra type; and 4) the seasonal patterns and magnitudes of leaf C and leaf N in deciduous and evergreen shrubs were responsive to conditions of deeper snow in winter. Leaf N is was generally higher immediately after emergence from the deep snow experimental treatments and leaf N was higher during the subsequent summer and fall, and the leaf C:N were lower, especially in deciduous shrubs. These findings indicate that coupled increases in snow depth and warmer summer temperatures will alter the magnitudes and patterns of leaf mineral nutrition and that the long term consequences of these changes may feed‐forward and affect ecosystem processes.
Leaf mass loss in wetland graminoids during senescence
Authors: Vernescu Corina , Coulas Jess , Ryser Peter
Published: February 2005

Mass loss of senescing leaves is an important part of plant biomass turnover and has consequences for assessment of ecosystem productivity, ecosystem nutrient use efficiency, and plant nutrient resorption efficiency. Data, however, on mass loss are scarce, and often based on leaf area as the reference base. This leads to an underestimation of the mass loss, as leaf area itself shrinks during senescence. Furthermore, the few existing studies have almost exclusively used woody species. The purpose of the present study was twofold: i) to assess leaf mass loss during senescence in herbaceous species, with the example of five wetland graminoids and, ii) to compare two different methods of mass loss assessment (two species). Assuming that leaf length does not change during senescence, we assessed leaf mass per leaf length prior to and after senescence. We also estimated pre‐senescence leaf mass nondestructively based on leaf length, width and thickness. For Typha latifolia and Carex stricta, two species with graminoid type leaves but contrasting leaf structure, both methods delivered almost identical results. After the first assessment of leaf mass on July 7th, T. latifolia leaf mass initially increased by 13%, and then decreased to be 12% below the original mass after senescence. C. stricta leaf mass remained stable until senescence, but decreased then by 33%. In a second experiment, the mass of 100 mm pieces of leaves was measured before and after senescence. Calamagrostis canadensis, Carex rostrata and C. stricta lost 23–57% of their leaf mass during senescence, whereas Glyceria canadensis did not show any mass loss. We conclude that mass loss of senescing leaves of herbaceous plants can be considerable and should not be neglected in studies of productivity, nutrient use efficiency or nutrient resorption. For species with no shrinking leaf length during senescence, mass loss can be measured with leaf length as the base whereas for others, pre‐senescent mass can be estimated on the basis of leaf dimensions.
The importance of importance
Authors: Brooker Rob , Kikvidze Zaal , Pugnaire Francisco I. , Callaway Ragan M. , Choler Philippe , Lortie Christopher J. , Michalet Richard
Published: February 2005

Failure to distinguish between ‘importance’ and ‘intensity’ of competition has hindered our ability to resolve key questions about the role interactions may play in plant communities. Here we examine how appropriate application of metrics of importance and intensity is integral to investigating key theories in plant community ecology and how ignoring this distinction has lead to confusion and possibly spurious conclusions. We re‐explore the relationship between competition intensity and importance for individuals across gradients, and apply our review of concepts to published data to help clarify the debate. We demonstrate that competition importance and intensity need not be correlated and show how explicit application of the intensity and importance of competition may reconcile apparently incompatible paradigms.
The relative importance of spatial aggregation and resource partitioning on the coexistence of mycophagous insects
Authors: Takahashi Kazuo H. , Tuno Nobuko , Kagaya Takashi
Published: February 2005

The relative importance of spatial aggregation and resource partitioning on coexistence was investigated for mycophagous insects in central Japan. The effects of spatial aggregation and resource partitioning were separated by a randomization procedure. From 124 patches of macrosporophores belonging to 37 species, 3275 individuals belonging to 14 families of Diptera and 11 individuals to Lepidoptera emerged. Since the level of identification varied among insect taxa, the analysis was made in three ways; 1) for all taxa to assess the stability of the whole community, 2) for drosophilid species to assess their persistence in the community, and 3) for species of Drosophila and Mycodrosophila to assess their persistence against congeneric and heterogeneric species. Both spatial aggregation and resource partitioning functioned for the stability of whole mycophagous insect community, and spatial aggregation played a more important role than resource partitioning. On the other hand, only spatial aggregation functioned for the persistence of drosophilid species in the community. According to the analysis on species of Drosophila and Mycodrosophila against congeneric and heterogeneric species, the relative importance of resource partitioning was smaller for the coexistence of within‐genus species pairs than for that of between‐genus species pairs. These results suggest that the relative importance of these two mechanisms depends on the phylogenetic and guild diversity of community.
Opposite relationships between invasibility and native species richness at patch versus landscape scales
Authors: Knight Kathleen S. , Reich Peter B.
Published: February 2005

Using a nested plot design in oak forests in Minnesota, USA we measured the percent cover of young individuals of an exotic invading shrub,Rhamnus cathartica(common buckthorn), to assess the relationships at two scales between invasibility, propagule and light availability, and richness and cover of native species. Comparing patches (1 m2) within 17Quercus‐dominated stands (each 1 ha, within a 100 km by 150 km area), cover of youngR. catharticawas negatively related to both species richness and cover of native species. In 1 m2patches, native cover was positively associated with native richness and thus cover‐related competition was a likely mechanism by which richness influencedR. cathartica. At the landscape scale (comparing the aggregate stand‐scale metrics among the 17 stands), native cover and richness were still positively related, but had opposite relationships withR. catharticacover.R. catharticacover was positively related to species richness and negatively related to native species cover. The observed switch at different scales from a positive to a negative relationship betweenR. catharticacover and native richness supported the hypothesized scale dependence of these relations. Propagule pressure, which we estimated by measuring the size of nearby matureR. catharticashrubs, had a large positive effect onR. catharticaseedling cover at the landscape scale. These results suggest that landscape patterns of invasion may be best understood in light of the combination of many factors including native diversity, native cover, and propagule pressure.
Carry‐over effects and habitat quality in migratory populations
Authors: Norris D. Ryan
Published: February 2005

Determining the factors that influence migratory population abundance has been constrained by the inability to connect events in different periods of the annual cycle. Carry‐over effects are events that occur in one season but influence individual success the following season and recent empirical evidence suggests that they may play an important role in migratory population dynamics. Using a long distance migratory shorebird as an example, I incorporate carry‐over effects and changes in the relative amount of habitat quality into a density‐dependent equilibrium population model. The model uses the example where the quality of habitat on the wintering grounds (nonbreeding season) influences breeding output the following summer (breeding season). Carry‐over effects, however, may be manifested in a number of other ways that could influence population dynamics. In the simulations, population declines occur when habitat is lost on the wintering grounds. However, results show that carry‐over effects can magnify these declines when a disproportionate amount of high quality habitat is lost the previous winter. Simulations also show that carry‐over effects can have a relative, positive impact on population size when the majority of habitat that is lost in the previous season is low quality. In this case, the carry‐over interacts with density‐dependence the following season producing an additive and positive effect, buffering the population from severe declines. To predict changes in population size of migratory animals, it will be important to determine (i) which demographic factors in which season produce strong carry‐over effects and, (ii) not just the amount, but the relative quality of habitat that is lost. If carry‐over effects are significant, they could potentially mitigate ‘seasonal compensation effects’ from density‐dependence, leading to exacerbated population declines.
Marine subsidies alter the diet and abundance of insular and coastal lizard populations
Authors: Barrett Kyle , Anderson Wendy B. , Wait D. Alexander , Grismer L. Lee , Polis Gary A. , Rose Michael D.
Published: February 2005

We evaluated the impact of marine materials on the diet and abundance of arthropodivorous lizards inhabiting islands and the coast of the Gulf of California. Here, marine materials are brought onto land by seabirds and by tidal action, and both subsidy pathways cause arthropod abundance to increase. We evaluated Uta stansburiana (side‐blotched lizard) diets in three habitats defined by having: (1) no marine subsidies available, (2) only seabird‐derived subsidies, and (3) only tidal‐derived subsidies. Stable isotope data indicated that lizard diets are subsidized indirectly by seabird and tidal activity. For example, in coastal areas we determined that 40% of a lizard's diet contains arthropods that have consumed algae. Such subsidies may explain why we found that lizards in coastal areas occupy a significantly higher trophic position than lizards in unsubsidized areas. We analyzed eight years of survey data on all arthropodivorous lizards to determine if diet subsidies result in increased lizard abundance. We found that lizards were more abundant in coastal areas than they were in inland habitats, and that they were more abundant on islands with seabirds than on islands without seabird populations. This study provides insight into the importance and effect of marine‐derived nutrients from multiple sources on vertebrate consumers inhabiting islands and coastal areas.