Spin Conduction in Anisotropic 3-D Topological Insulators

When topological insulators possess rotational symmetry their spin lifetime is tied to the scattering time. We show that in anisotropic TIs this tie can be broken and the spin lifetime can be very large. Two different mechanisms can obtain spin conduction over long distances. The first is tuning the Hamiltonian to conserve a spin operator $\cos \phi \, \sigma_x + \sin \phi \, \sigma_y$, while the second is tuning the Fermi energy to be near a local extremum of the energy dispersion. Both mechanisms can produce persistent spin helices. We report spin lifetimes and spin diffusion equations.Comment: Added a page of additional text and refined the presentation. Main content unchange

Exercise-induced sweat nitrogen excretion: evaluation of a regional collection method using gauze pads

Summary: The exercise-induced sweat nitrogen excretion was investigated during a 45-minute run at moderate intensity on a treadmill. Sweat was collected with a regional collection technique using gauze pads and compared with the whole-body wash-down (WBW) method. In the regional collection, sweat was sampled from the upper back (UB), lower back (LB), abdomen (AB), and thigh (TH). Additionally, the relation of sweat urea, ammonia, and amino acids was investigated with the regional collection method during a second 45-minute run. Independent of the sweat collection method, a significant and positive correlation was found between sweat rate and the excretion rate of the largest nitrogen fraction urea, suggesting that the sweating response to exercise might be one of the most important factors determining absolute sweat nitrogen losses. The urea nitrogen excretion was nearly 140 mg·h−1 in the second run, representing the largest nitrogen fraction. Ammonia nitrogen and amino acid-derived nitrogen rate were approximately 30 mg·h−1 and 10 mg·h−1, respectively. The comparison of the sampling methods during the first run revealed that the urea nitrogen rate was significantly higher, but the ammonia nitrogen rate significantly lower in the WBW. After summing urea and ammonia nitrogen, no significant difference between the methods was observed anymore, except for UB. It is concluded that the regional collection method using gauze pads is a valuable approach to measure exercise-induced sweat nitrogen losses during moderate running exercis

The effects of dietary mannaoligosaccharides on cecal parameters and the concentrations of enteric bacteria in the ceca of salmonella-challenged broiler chicks

The ability of different enteric pathogens and coliforms to trigger agglutination of yeast cells (Saccharomyces cerevisiae, NCYC 1026) and a yeast cell wall preparation (MOS) was examined. Five of seven strains of Escherichia coli and 7 of 10 strains of Salmonella typhimurium and Salmonella enteritidis agglutinated MOS and Sac. cerevisiae cells. Strains of Salmonella choleraesuis, Salmonella pullorum, and Campylobacter did not lead to agglutination. Two strains that agglutinated MOS (S. typhimurium 29E and Salmonella dublin) and one nonagglutinating strain (S. typhimurium 27A) were selected as challenge organisms for in vivo studies in chicks under controlled conditions. In a series of three trials in which 3-d-old chicks were orally challenged with 10(4) cfu of S. typhimurium 29E, birds receiving 4,000 ppm of dietary MOS had reduced cecal S. typhimurium 29E concentrations (5.40 vs 4.01 log cfu/ g; P < 0.05) at Day 10. In a second series of three trials with S. dublin as challenge organism, the number of birds that tested salmonella positive in the ceca at Day 10 was less when MOS was part of the diet (90 vs 56%; P < 0.05). To test the effect of MOS on concentrations of bacteria that do not express Type 1 fimbriae, a challenge trial was conducted with S. typhimurium 27A. However, strain 27A did not colonize the birds sufficiently to evaluate whether MOS affected its cecal concentration. Mannanoligosaccharide did not significantly reduce the concentrations of cecal coliforms (P < 0.10) although they were numerically lower. It had no effect on cecal concentrations of lactobacilli, enterococci, anaerobic bacteria, lactate, volatile fatty acid, or cecal p

Effect of Pelleting Temperature on the Activity of Different Enzymes

The effects of different pelleting temperatures on the activity of cellulase, bacterial amylase, fungal amylase, and pentosanase were tested. Samples of a commercial barley-wheat-soybean diet containing different enzyme preparations were pelleted at 60, 70, 80, 90, and 100 C (pellet temperature measured at the die outlet) through a die containing holes 2.5 mm in diameter. Enzymatic analyses were conducted on either soluble substrates or by measuring the ability of the tested enzymes to decrease the viscosity of the diet. Measurements made on soluble substrates suggest that cellulase, fungal amylase, and pentosanase maintained activity when being pelleted at temperatures up to 80 C and bacterial amylase maintained activity at temperatures up to 90 C. Pentosanase and amylases showed little or no effect on the viscosity of the diet. Cellulase addition decreased the viscosity at all temperature levels, even after being pelleted at 90 and 100 C (P < 0.05). No cellulolytic activity was detected on the soluble substrate after these pelleting temperatures. Measurements on a soluble substrate might therefore not always reflect the true stability of a preparation because the ability of a carbohydrase to decrease the viscosity of the digesta is important to its effect in the gastrointestinal tract. Measurements on soluble substrates suggest that cellulase, fungal amylase, and pentosanase can be pelleted at temperatures up to at least 80 C and bacterial amylase up to 90 C without a considerable loss in analyzed activit

Spin response to localized pumps:Exciton polaritons versus electrons and holes

Polariton polarization can be described in terms of a pseudospin which can be oriented along the x,y, or z axis, similarly to electron and hole spin. Unlike electrons and holes where time-reversal symmetry requires that the spin-orbit interaction be odd in the momentum, the analog of the spin-orbit interaction for polaritons, the so-called TE-TM splitting, is even in the momentum. We calculate and compare spin transport of polariton, electron, and hole systems, in the diffusive regime of many scatterings. After dimensional rescaling diffusive systems with spatially uniform particle densities have identical dynamics, regardless of the particle type. Differences between the three particles appear in spatially nonuniform systems, with pumps at a specific localized point. We consider both oscillating pumps and transient (delta function) pumps. In such systems each particle type produces distinctive spin patterns. The particles can be distinguished by their differing spatial multipole character, their response and resonances in a perpendicular magnetic field, and their relative magnitude which is largest for electrons and weakest for holes. These patterns are manifested both in response to unpolarized pumps which produce in-plane and perpendicular spin signals, and to polarized pumps where the spin precesses from in-plane to out-of-plane and vice versa. These results will be useful for designing systems with large spin polarization signals, for identifying the dominant spin-orbit interaction and measuring subdominant terms in experimental devices, and for measuring the scattering time and the spin-orbit coupling's magnitude.Published versio

Neutral magic-angle bilayer graphene: Condon instability and chiral resonances

We discuss the full optical response of twisted bilayer graphene at the neutrality point close to the magic angle within the continuum model. (i) First, we define the full optical response consistent with the underlying $D_3$ symmetry, yielding the total, magnetic, and chiral response that transform according to the irreducible representations $A_1$, $A_2$, and $E$, respectively. Then, we numerically calculate the dissipative and reactive response for twist angles around the magic angle $\theta_m$ and comment on the possibility of a Condon instability. (ii) Second, we numerically calculate the full optical response {\it almost at} $\theta_m$. The total response is characterized by three universal plateaus which can be obtained from an analytical calculation. The magnetic and the chiral response, however, is given by corresponding non-universal plateaus depending on the twist angle $\theta$ via the dimensionless parameter $\alpha\sim\theta_m-\theta$. (iii) Following the discussion on the large magnetic response, we calculate the plasmonic excitations at the neutrality point inside the optical gap of relaxed twisted bilayer graphene. We find that acoustic plasmons extend over almost the whole optical gap and carry the largest oscillator strength. (iv) Finally, we discuss symmetry relations for the response functions as function of the chemical potential and highlight the consequences of the approximate particle-hole symmetry of the continuum model for twisted bilayer graphene. We then discuss a detailed balance relation where the chiral response at charge neutrality can be understood in terms of electron (hole) transitions for which the initial (final) states are energetically closer to charge neutrality than the final (initial) states.Comment: 17 pages, 7 figure

Spin Hall Conductivity on the Anisotropic Triangular Lattice

We present a detailed study of the spin Hall conductivity on a two-dimensional triangular lattice in the presence of Rashba spin-orbit coupling. In particular, we focus part of our attention on the effect of the anisotropy of the nearest neighbor hopping amplitude. It is found that the presence of anisotropy has drastic effects on the spin Hall conductivity, especially in the hole doped regime where a significant increase or/and reversed sign of the spin Hall conductivity has been obtained. We also provide a systematic analysis of the numerical results in terms of Berry phases. The changes of signs observed at particular density of carriers appear to be a consequence of both Fermi surface topology and change of sign of electron velocity. In addition, in contrast to the two-dimensional square lattice, it is shown that the tight binding spin-orbit Hamiltonian should be derived carefully from the continuous model on the triangular lattice.Comment: 8 pages, 10 figure