Transport of Cosmic Rays in Chaotic Magnetic Fields

The transport of charged particles in disorganised magnetic fields is an important issue which concerns the propagation of cosmic rays of all energies in a variety of astrophysical environments, such as the interplanetary, interstellar and even extra-galactic media, as well as the efficiency of Fermi acceleration processes. We have performed detailed numerical experiments using Monte-Carlo simulations of particle propagation in stochastic magnetic fields in order to measure the parallel and transverse spatial diffusion coefficients and the pitch angle scattering time as a function of rigidity and strength of the turbulent magnetic component. We confirm the extrapolation to high turbulence levels of the scaling predicted by the quasi-linear approximation for the scattering frequency and parallel diffusion coefficient at low rigidity. We show that the widely used Bohm diffusion coefficient does not provide a satisfactory approximation to diffusion even in the extreme case where the mean field vanishes. We find that diffusion also takes place for particles with Larmor radii larger than the coherence length of the turbulence. We argue that transverse diffusion is much more effective than predicted by the quasi-linear approximation, and appears compatible with chaotic magnetic diffusion of the field lines. We provide numerical estimates of the Kolmogorov length and magnetic line diffusion coefficient as a function of the level of turbulence. Finally we comment on applications of our results to astrophysical turbulence and the acceleration of high energy cosmic rays in supernovae remnants, in super-bubbles, and in jets and hot spots of powerful radio-galaxies.Comment: To be published in Physical Review D, 20 pages 9 figure

Development of an X-band Photoinjector at SLAC

As part of a National Cancer Institute contract to develop a compact source of monoenergetic X-rays via Compton backscattering, we have completed the design and construction of a 5.5 cell Photoinjector operating at 11.424 GHz. Successful completion of this project will result in the capability of generating a monoenergetic X-ray beam, continuously tunable from 20 - 85 KeV. The immediate goal is the development of a Photoinjector producing 7 MeV, 0.5 nC, sub-picosecond electron bunches with normalized RMS emittances of approximately 1 pi-mm-mR at repetition rates up to 60 Hz. This beam will then be further accelerated to 60 MeV using a 1.05 m accelerating structure. This Photoinjector is somewhat different than the traditional 1.5 cell design both because of the number of cells and the symmetrically fed input coupler cell. Its operating frequency is also unique. Since the cathode is non-removable, cold-test tuning was somewhat more difficult than in other designs. We will present results of "bead-drop" measurements used in tuning this structure. Initial beam measurements are currently in progress and results will be presented as well as results of RF conditioning to high gradients at X-band. Details of the RF system, emittance-compensating solenoid, and cathode laser system as well as PARMELA simulations will also be presented.Comment: 3 pages, 6 figures, 1 Table, LINAC 200

Inhibition of Tendon Cell Proliferation and Matrix Glycosaminoglycan Synthesis by Non-Steroidal Anti-Inflammatory Drugs in vitro

The purpose of this study was to investigate the effects of some commonly used non-steroidal anti-inflammatory drugs (NSAIDs) on human tendon. Explants of human digital flexor and patella tendons were cultured in medium containing pharmacological concentrations of NSAIDs. Cell proliferation was measured by incorporation of 3H-thymidine and glycosaminoglycan synthesis was measured by incorporation of 35S-Sulphate. Diclofenac and aceclofenac had no significant effect either on tendon cell proliferation or glycosaminoglycan synthesis. Indomethacin and naproxen inhibited cell proliferation in patella tendons and inhibited glycosaminoglycan synthesis in both digital flexor and patella tendons. If applicable to the in vivo situation, these NSAIDs should be used with caution in the treatment of pain after tendon injury and surgery

Chronic sciatic nerve injury impairs the local cutaneous neurovascular interaction in rats

Most studies of chronic nerve compression focus on large nerve function in painful conditions, and only few studies have assessed potential changes in the function of small nerve fibers during chronic nerve compression and recovery from compression. Cutaneous pressure-induced vasodilation is a neurovascular phenomenon that relies on small neuropeptidergic fibers controlling the cutaneous microvasculature. We aimed to characterize potential changes in function of these small fibers and/or in cutaneous microvascular function following short-term (1-month) and long-term (6-month) nerve compression and after release of compression (ie, potential recovery of function). A compressive tube was left on one sciatic nerve for 1 or 6 months and then removed for 1-month recovery in Wistar rats. Cutaneous vasodilator responses were measured by laser Doppler flowmetry in hind limb skin innervated by the injured nerve to assess neurovascular function. Nociceptive thermal and low mechanical thresholds were evaluated to assess small and large nerve fiber functions, respectively. Pressure-induced vasodilation was impaired following nerve compression and restored following nerve release; both impairment and restoration were strongly related to duration of compression. Small and large nerve fiber functions were less closely related to duration of compression. Our data therefore suggest that cutaneous pressure-induced vasodilation provides a non-invasive and mechanistic test of neurovascular function that gives direct information regarding extent and severity of damage during chronic nerve compression and recovery, and may ultimately provide a clinically useful tool in the evaluation of nerve injury such as carpal tunnel syndrome

The effects of chest wall loading on perceptions of fatigue, exercise performance, pulmonary function, and muscle perfusion.

BACKGROUND: Load carriage (LC), which directly affects the chest wall and locomotor muscles, has been suggested to alter the ventilatory and circulatory responses to exercise, leading to increased respiratory muscle work and fatigue. However, studies exploring the impact of LC on locomotion increased internal work, complicating their interpretation. To overcome this issue, we sought to determine the effect of chest wall loading with restriction (CWL + R) on cycling performance, cardiopulmonary responses, microvascular responsiveness, and perceptions of fatigue. METHODS: In a randomized crossover design, 23 young healthy males (22 \ub1 4 years) completed a 5 km cycling time trial (TT) in loaded (CWL + R; tightened vest with 10% body weight) and unloaded conditions. After baseline pulmonary function testing (PFT; forced expiratory volume in 1 s, FEV1; forced vital capacity, FVC), cardiopulmonary indices (HR, heart rate; O2 uptake, VO2; ventilation, VE; tidal volume, VT; and breathing frequency, Bf), rating of perceived exertion (RPE), lactate (BLa), and microvascular responses (oxy-, deoxy-, total hemoglobin; and tissue saturation; StO2) of the vastus lateralis using near infrared spectroscopy were collected during the TT; and PFT was repeated post-exercise. RESULTS: Pre-exercise, CWL + R reduced (p < 0.05) FVC (5.6 \ub1 0.8 versus 5.5 \ub1 0.7 L), FEV1 (4.8 \ub1 0.7 versus 4.7 \ub1 0.6 L), and FEV1/FVC (0.9 \ub1 0.1 versus 0.8 \ub1 0.1). CWL + R modified power output (PO) over time (interaction, p = 0.02), although the 5 km time (461 \ub1 24 versus 470 \ub1 27 seconds), VT (3.0 \ub1 0.3 versus 2.8 \ub1 0.8 L), Bf, VE, HR, VO2, microvascular and perceptual (visual analog scale, or VAS, and RPE) responses were unchanged (p > 0.05). CWL + R increased (p < 0.05) the average BLa (7.6 \ub1 2.6 versus 8.6 \ub1 3 mmol/L). CONCLUSIONS: Modest CWL + R negatively affects pre-exercise pulmonary function, modifies cycling power output over time, and increases lactate production during a 5 km cycling trial, although the cardiorespiratory, microvascular, and perceptual responses were unaffected

Estimating the functional form for the density dependence from life history data

Two contrasting approaches to the analysis of population dynamics are currently popular: demographic approaches where the associations between demographic rates and statistics summarizing the population dynamics are identified; and time series approaches where the associations between population dynamics, population density, and environmental covariates are investigated. In this paper, we develop an approach to combine these methods and apply it to detailed data from Soay sheep (Ovis aries). We examine how density dependence and climate contribute to fluctuations in population size via age- and sex-specific demographic rates, and how fluctuations in demographic structure influence population dynamics. Density dependence contributes most, followed by climatic variation, age structure fluctuations and interactions between density and climate. We then simplify the density-dependent, stochastic, age-structured demographic model and derive a new phenomenological time series which captures the dynamics better than previously selected functions. The simple method we develop has potential to provide substantial insight into the relative contributions of population and individual-level processes to the dynamics of populations in stochastic environments

Rocaglates induce gain-of-function alterations to eIF4A and eIF4F

Rocaglates are a diverse family of biologically active molecules that have gained tremendous interest in recent years due to their promising activities in pre-clinical cancer studies. As a result, this family of compounds has been significantly expanded through the development of efficient synthetic schemes. However, it is unknown whether all of the members of the rocaglate family act through similar mechanisms of action. Here, we present a comprehensive study comparing the biological activities of >200 rocaglates to better understand how the presence of different chemical entities influences their biological activities. Through this, we find that most rocaglates preferentially repress the translation of mRNAs containing purine-rich 5' leaders, but certain rocaglates lack this bias in translation repression. We also uncover an aspect of rocaglate mechanism of action in which the pool of translationally active eIF4F is diminished due to the sequestration of the complex onto RNA.P50 GM067041 - NIGMS NIH HHS; R24 GM111625 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HHSPublished versio

An asteroseismic test of diffusion theory in white dwarfs

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. We have obtained dual-site observations of the pulsating DB star CBS114, to complement existing observations of the slightly cooler star GD358. We recover the 7 independent pulsation modes that were previously known, and we discover 4 new ones to provide additional constraints on the models. We perform objective global fitting of our updated double-layered envelope models to both sets of observations, leading to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG1159 stars.Comment: 7 pages, 3 figures, 3 tables, accepted for publication in A&

Now or never: perceptions of uniqueness induce acceptance of price increases for experiences more than for objects

Seven studies test and support the prediction that consumers are more willing to accept a price increase for an experiential versus a material purchase; an effect explained by the greater uniqueness of experiences. Critically, the uniqueness model advanced here is found to be independent of the happiness consumers derive from the purchase. To gain a deeper understanding of the uniqueness mechanism, this investigation then advances and tests a four-facet framework of uniqueness (unique opportunity, unique purchase, unique identity, and counterconformity). Together, the findings converge on the conclusion that consumers perceive the opportunity to have a particular experience (vs. object) as more unique, and this unique opportunity increases their willingness to accept a price increase. Overall, this work extends the experiential versus material purchases literature into a new domain—that of pricing; identifies the dimension—uniqueness—and its precise facet responsible for the effect—unique opportunity; and demonstrates that this model unfolds in a pattern distinct from the oft researched model centered on consumer happiness. Theoretical and practical implications are discussed.info:eu-repo/semantics/acceptedVersio