Meissner response of anisotropic superconductors

The response field of a half-space anisotropic superconductor is evaluated for an arbitrary weak external field source. Example sources of a point magnetic moment and a circular current are considered in detail. For the penetration depth $\lambda \ll L$ with $L$ being any other relevant distance (the source size, or the distance between the source and the superconductor), the major contribution to the response is the $\lambda$ independent field of the source image. It is shown that the absolute value of $\lambda$ cannot be extracted from the response field with a better accuracy than that for the source position. Similar problems are considered for thin films.Comment: 8 pages, 0 figures. 7 pages: section removed, refs. adde

Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets

The nonlinear ac stationary response of uniaxial paramagnets and superparamagnets - nanoscale solids or clasters with spin number S ~ 10^0 - 10^4 - in superimposed uniform ac and dc bias magnetic fields of arbitrary strength, each applied along the easy axis of magnetization, is determined by solving the evolution equation for the reduced density matrix represented as a finite set of three-term differential-recurrence relations for its diagonal matrix elements. The various harmonic components of the magnetization, dynamic magnetic hysteresis loops, etc. are then evaluated via matrix continued fractions indicating a pronounced dependence of the nonlinear response on S arising from the quantum spin dynamics. In the linear response approximation, the results concur with existing solutions.Comment: 28 pages, 10 figures, 33 refererence

Scheduling effects of 5-(3,3-Dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) and 1,3-Bis-chloroethyl-1-nitrosourea (BCNU) on mouse melanoma cells B16CL5

DTIC and BCNU have been demonstrated to have enhanced chemotherapeutic effects in mice bearing Bl6 mouse melanoma cells. The order of administration seems to be important in maintaining optimum effects. This was shown is a study by Hill et al. (unpublished). In the present study, mouse melanoma cells, Bl6CL4, were treated with either DTIC or BCNU. The drug was allowed to remain on the cells for 2, 3, or 4 days. The drug-containing media were then removed, the cells were washed and fresh medium was added. The cells were incubated in an atmosphere of 5% CO2 and 95% air at 37 °C. In combination experiments, dishes of B16CL4 cells were treated with DTIC on day 0. BCNU was then added on days 0, 1, or 2 of exposure. At the end of the allotted time the drug-containing media were removed and replaced with fresh medium. The dishes were incubated under the same conditions as those used for the controls. This procedure was repeated except that BCNU was added first and DTIC was added on day 0, 1, or 2 of exposure. The dishes were incubated for 15 days and the colonies were then fixed and stained. All colonies containing 50 cells or more were counted. The results showed that DTIC alone enhanced cell death the longer it remained in contact with the cells. BCNU alone had no effect at the concentration used. The results for the dose schedule when DTIC was added on day 0, followed by BCNU on day 2, showed a 60% decrease in the observed surviving fraction of cells from the expected surviving fraction of cells. This indicated that melanoma cell death was enhanced and these results are in agreement with the previous study conducted by Hill et al. (unpublished). The results for the dose schedule when BCNU was added on day 0, followed by DTIC on day 1, showed a 66% decrease in the observed surviving fraction of cells from the expected surviving fraction of cells. But then, the decrease in observed surviving fraction of cells from the expected surviving fraction of cells rose from 66% to 26%. These results were similar to the in vivo results seen in the study conducted by Hill et al. (21). However, these in vivo effects were not as dramatic as the effects seen when DTIC was added first

Magnetization dynamics of two interacting spins in an external magnetic field

The longitudinal relaxation time of the magnetization of a system of two exchange coupled spins subjected to a strong magnetic field is calculated exactly by averaging the stochastic Gilbert-Landau-Lifshitz equation for the magnetization, i.e., the Langevin equation of the process, over its realizations so reducing the problem to a system of linear differential-recurrence relations for the statistical moments (averaged spherical harmonics). The system is solved in the frequency domain by matrix continued fractions yielding the complete solution of the two-spin problem in external fields for all values of the damping and barrier height parameters. The magnetization relaxation time extracted from the exact solution is compared with the inverse relaxation rate from Langer's theory of the decay of metastable states, which yields in the high barrier and intermediate-to-high damping limits the asymptotic behaviour of the greatest relaxation time.Comment: 32 pages, 5 figures. The paper has been revised and new results added (e.g., Fig. 5

Stochastic dynamics beyond the weak coupling limit: thermalization

We discuss the structure and asymptotic long-time properties of coupled equations for the moments of a Brownian particle's momentum derived microscopically beyond the lowest approximation in the weak coupling parameter. Generalized fluctuation-dissipation relations are derived and shown to ensure convergence to thermal equilibrium at any order of perturbation theory.Comment: 6+ page

Thermally activated escape rates of uniaxial spin systems with transverse field

Classical escape rates of uniaxial spin systems are characterized by a prefactor differing from and much smaller than that of the particle problem, since the maximum of the spin energy is attained everywhere on the line of constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is applied, a saddle point of the energy is formed, and high, moderate, and low damping regimes (similar to those for particles) appear. Here we present the first analytical and numerical study of crossovers between the uniaxial and other regimes for spin systems. It is shown that there is one HD-Uniaxial crossover, whereas at low damping the uniaxial and LD regimes are separated by two crossovers.Comment: 4 PR pages, 3 figures, final published versio

Magnetic susceptibility of a CuO2 plane in the La2CuO4 system: I. RPA treatment of the Dzyaloshinskii-Moriya Interactions

Motivated by recent experiments on undoped La2CuO4, which found pronounced temperature-dependent anisotropies in the low-field magnetic susceptibility, we have investigated a two-dimensional square lattice of S=1/2 spins that interact via Heisenberg exchange plus the symmetric and anti-symmetric Dzyaloshinskii-Moriya anisotropies. We describe the transition to a state with long-ranged order, and find the spin-wave excitations, with a mean-field theory, linear spin-wave analysis, and using Tyablikov's RPA decoupling scheme. We find the different components of the susceptibility within all of these approximations, both below and above the N'eel temperature, and obtain evidence of strong quantum fluctuations and spin-wave interactions in a broad temperature region near the transition.Comment: 20 pages, 2 column format, 22 figure

Transient rectification of Brownian diffusion with asymmetric initial distribution

In an ensemble of non-interacting Brownian particles, a finite systematic average velocity may temporarily develop, even if it is zero initially. The effect originates from a small nonlinear correction to the dissipative force, causing the equation for the first moment of velocity to couple to moments of higher order. The effect may be relevant when a complex system dissociates in a viscous medium with conservation of momentum

Dual Ion Spectrometers and Their Calibration for the Fast Plasma Investigation on NASA's Magnetospheric Multiscale Mission

The scientific target of NASA's Magnetospheric Multiscale (MMS) mission is to study the fundamentally important phenomenon of magnetic reconnection. Theoretical models of this process predict a small size, on the order of hundred kilometers, for the ion diffusion region where ions are demagnetized at the dayside magnetopause. This region may typically sweep over the spacecraft at relatively high speeds of 50 km/s, requiring the fast plasma investigation (FPI) instrument suite to have an extremely high time resolution for measurements of the 3D particle distribution functions. As part of the FPI on MMS, the 16 dual ion spectrometers (DIS) will provide fast (150 ms) 3D ion velocity distributions, from 10 to 30,000 eV/q, by combining the measurements from four dual spectrometers on each of four MMS spacecraft. For any multispacecraft mission, the response uniformity among the spectrometer set assumes an enhanced importance. Due to these demanding instrument requirements and the effort of calibrating more than 32 sensors (16 2) within a tight schedule, a highly systematic and precise calibration was required for measurement repeatability. To illustrate how this challenge was met, a brief overview of the FPI DIS was presented with a detailed discussion of the calibration method of approach and implementation. Finally, a discussion of DIS performance results, their unit-to-unit variation, and the lessons learned from this calibration effort are presented

Molecular bases of training adaptation

The molecular events that promote or inhibit specific training adaptations (i.e. skeletal muscle hypertrophy or mitochondrial biogenesis) are not completely understood. Accordingly, there is a need to better define both the acute and chronic responses to divergent exercise stimuli in order to elucidate the specific molecular mechanisms that ultimately determine skeletal muscle phenotype. Therefore, the primary aims of the studies undertaken for this thesis were to examine the acute molecular adaptation responses in skeletal muscle following resistance and endurance training. In order to determine the acute molecular events following repeated bouts of exercise, the study described in Chapter Two compared a high-frequency stacked training regimen designed to generate a summation of transient exercise-induced signalling responses with a conventional-frequency resistance training protocol. Groups (n= 6) of Sprague-Dawley rats performed either high-frequency training (four exercise bouts consisting of 3 - 10 repetitions separated by 3 h) or conventional-frequency training (three exercise bouts consisting of 4 - 10 repetitions with 48 h between sessions). Protocols were matched for total work, and repetitions were performed at 75% one-repetition maximum with 3 min recovery between sets. White quadriceps muscle was extracted 3 h after every training bout, and 24 and 48 h following the final exercise session of each protocol. AKT phosphorylation was significantly decreased 3 h following the 2nd bout of high-frequency training, an effect that persisted until 48 h after the final exercise bout (P less than 0.05), while the phosphorylation state of this kinase was unchanged with conventional training. These results suggest that high-frequency training suppressed IGF-1 mediated signalling. Furthermore, high-frequency training generated sustained and coordinated increases in TNFá and IKK phosphorylation (P less than 0.05), indicating an extended response of inflammatory signalling pathways. Conversely, and irrespective of an initial increase after the first bout of exercise, TNFá signalling ultimately returned to control Abstract values by DAY 5 of conventional-frequency training, indicative of a rapid adaptation to the exercise stimulus. Notably, despite differential AKT activation there were similar increases in p70 S6K phosphorylation with both training protocols. These results indicate high-frequency resistance training extends the transient activation of inflammatory cytokine-mediated signalling and results in a persistent suppression of AKT phosphorylation, but these events do not appear to inhibit kinase activity proximal to translation initiation. The aim of the study described in Chapter Three was to determine the effect of prior training history on selected signalling responses after an acute bout of resistance and endurance exercise. Following 24 h diet / exercise control 13 male subjects (7 strength-trained and 6 endurance-trained) performed a random order of either resistance (8 x 5 maximal leg extensions) or endurance exercise (1 h cycling at 70% peak O2 uptake). Muscle biopsies were taken from the vastus lateralis at rest, immediately and 3 h post-exercise. AMPK phosphorylation increased after cycling in strength-trained, but not endurance-trained subjects (P less than 0.05). Conversely, AMPK was elevated following resistance exercise in endurance-, but not strength-trained subjects (P less than 0.05). Thus, AMPK was elevated only when subjects undertook a bout of exercise in a mode of training to which they were unaccustomed. Surprisingly, there was no change in AKT phosphorylation following resistance exercise regardless of the training background of the subjects. In the absence of increased AKT phosphorylation, resistance exercise induced an increase in p70 S6K and ribosomal S6 protein phosphorylation in endurance-trained but not strength-trained subjects (Pless than 0.05). AKT phosphorylation was increased in endurance-trained, but not strength-trained subjects after cycling (P less than 0.05). These results show that a degree of signalling &quot;response plasticity&quot; capable of diverse adaptive compliance is conserved at opposite ends of the adaptation continuum. Furthermore, the adaptive phenotype associated with a prolonged training history alters the subsequent signalling responses with divergent exercise stimuli. The third study described in Chapter Four quantified the acute sub-cellular mRNA responses in muscle to habitual and unfamiliar exercise modes. This study employed the same subjects and protocols outlined in Chapter Three and analysis was performed on muscle biopsies taken at rest and 3 h after an exercise bout. Gene expression was analysed using Real-Time PCR with changes normalised relative to pre-exercise values. Following cycling exercise peroxisome proliferator activated receptor gamma co-activator-1 alpha, pyruvate dehydrogenase kinase 4 and vascular endothelial growth factor mRNA abundance was significantly increased in both endurance and strength-trained subjects (P less than 0.05). This finding indicates that the adaptive phenotype of these athletes did not produce a disparity in the mRNA response of these &#039;metabolic genes&#039;. Similarly, muscle atrophy F box protein (MAFBx) mRNA increased in both groups (P less than 0.05) suggesting that a prolonged endurance training stimulus may increase the activity of pathways involved in the regulation of muscle atrophy. Unexpectedly, MyoD and Myogenin mRNA increased in endurance-trained subjects after cycling. Accordingly, it seems plausible to suggest that these regulators of satellite cell activity may have additional roles in skeletal muscle metabolism. Finally, high-intensity resistance exercise did not induce any change in mRNA abundance of selected &#039;myogenic&#039; genes in either group of subjects, despite a decrease in MAFBx and Myostatin mRNA in endurance-trained subjects. It may be that in highly-trained athletes a greater volume or repeated bout effect is required to initiate anabolic gene expression. Taken collectively, these results indicate that prior training history can modify the acute mRNA changes in skeletal muscle in response to exercise. Indeed, the data indicate that independent of exercise mode, the gene responses in skeletal muscle from endurance-trained athletes are more sensitive to alterations in the cellular milieu than strength-trained subjects. In summary, the work from the studies undertaken for this thesis provides novel information regarding the effects of the frequency of the training stimulus on signalling responses in skeletal muscle. Specifically, high-frequency resistance training does not enhance anabolic signal transduction and may exacerbate inflammation and atrophy. In regard to the effects of prior contractile history on early signalling and mRNA responses, divergent exercise induces a mode specific molecular response that is altered by the training-induced phenotype of the muscle, highlighting the need for extensive training overload in highly trained athletes