Analysis of electric-field-induced spin splitting in wide modulation-doped quantum wells

We analyze the proper inclusion of electric-field-induced spin splittings in the framework of the envelope function approximation. We argue that the Rashba effect should be included in the form of a macroscopic potential as diagonal terms in a multiband approach rather than the commonly used Rashba term dependent on k and electric field. It is pointed out that the expectation value of the electric field in a subband is sometimes not unique because the expectation values can even have opposite signs for the spin-split subband components. Symmetric quantum wells with Dresselhaus terms and the influence of the interfaces on the spin splitting are also discussed. We apply a well established multiband approach to wide modulation-doped InGaSb quantum wells with strong built-in electric fields in the interface regions. We demonstrate an efficient mechanism for switching on and off the Rashba splitting with an electric field being an order of magnitude smaller than the local built-in field that determines the Rashba splitting. The implications of our findings for spintronic devices, in particular the Datta-Das spin transistor and proposed modifications of it, are discussed.Comment: Modified version, now published. 10 pages, 3 figures, 2 table

Propylene glycol energy supplementation during peripartal period in dairy cows and reproduction efficiency parameters

The aim of this work was to investigate the impact of two energy supplements based on propylene glycol in dairy cows diet on ovarian and follicular morphology, conception, insemination index and length of service period. A total number of 60 Holstein Friesian dairy cows, parity between 2-8, with an average milk production of 7000 kg/305 days of lactation were divided into three experimental groups (20 dairy cows per group). The first group of dairy cows was supplemented daily with "Energy-plus" (O1 group; 200 mL propylene-glycol supplement) and the second group was supplemented with "Ketal" (O2 group; 160 mL propylene-glycol supplement), two weeks before partus until 30 days post partum. The third experimental group were non supplemented dairy cows (O3, control group). Ultrasound examination of the reproductive system using real time echo camera Falco VET 100 (ESAOTE PieMedical, Holland, B-shaped scan with linear-array endorectal 5-8 MHz probe) was conducted on every animal starting from day 40 postpartum. The diameters of the ovaries (left and right) and of the dominant follicle(s) were recorded. Ultrasound testing was repeated on day 50 and 60 postpartum only in cows which in the meantime were not inseminated. Reproduction efficiency parameters (conception rate, number of inseminations and length of service period) were recorded individually. The statistical significance of the differences between groups was tested using ANOVA with LSD test at the level of significance p<0.05, chi-square test and Kaplan-Meier survival analysis (the length of service period). There was no significant impact of the propylene glycol supplementation on the ovarian and follicular morphology at the first ultrasound examination. At the second ultrasound examination there was a significant difference between left ovarian dominant follicle diameter in the control and supplemented dairy cows (1.67±0.53 vs 1.12±0.29 and 1.11±0.35 cm, p<0.05, O3 vs O1 and O2, respectively). The cumulative percentage of conception after the first and second insemination was 60%, 81% and 25% in groups O1, O2 and O3, respectively (p<0.05, chi-square test). The insemination index was lowest in group O2 and statistically significant differences were found between groups O2 and O3 (1.69±0.79 : 3.38±1.36, respectively, p<0,05). The length of the service period was significantly (p<0.05, LSD test) shorter in the O2 group (100±35 days) compared to groups O1 and O3 (168±59 and 157±52 days, respectively), that was confirmed by the Kaplan-Meier survival analysis of days open periods. The use of propylene glycol supplement in dairy cows diet during peripartal period induced higher percentage of pregnancy rates after the first and second insemination, significantly shortened the length of the service period and reduced the insemination index

Levels of insulin, insulin-like growth factor-I and thyroid hormones in relation to the body condition score changes in periparturient dairy cows

The objective of this study was to determine the levels of insulin, insulin like growth factor I (IGF-I) and thyroid hormones in relation to the body condition score (BCS) of periparturient dairy cows. The study was carried out on twenty Holstein-Friesian dairy cows with average milk production of 7000 L/305 days in the previous lactation, parity ranging from 2-4. All cows were BCS scored during the early dry period, 7±3 days before and after parturition. Based on the BCS at the early dry period, cows were divided in two groups: cows with high BCS (3.75- 4.25, HBCS, n=10), and cows with moderate BCS (2.75-3.75, MBCS, n=10). Blood samples were taken at the time of BCS evaluation. Concentrations of insulin, IGF-I, triiodothyroinine (T3) and thyroxine (T4) were determined by radioimmunoassay (RIA, INEP-Zemun, Serbia). Statistical differences between mean values were determined using Student t-test (p<0.01). Mean BCS values at early dry period were significantly different compared to two other periods (p<0.01) within both groups, but BCS was similar in both groups at 7±3 days after calving (2.69±0.67:2.62± 0.27, p>0.05). IGF-I level in HBCS cows at days 7±3 before calving was significantly higher (16.28±3.07:11.76±2.28, p<0.01), with a reverse relationship after calving (3.77±1.64:8.46±2.37, p<0.01). Insulin level was significantly lower at 7±3 days before calving in HBCS cows (16.26±4.60:20.18±4.96mIU/L, p<0.05). Thyroid hormones levels were significantly lower in HBCS group et all examined periods. [Projekat Ministarstva nauke Republike Srbije, br. III 46002 i br. 31003

Terahertz magneto-optical spectroscopy of two-dimensional hole and electron systems

We have used terahertz (THz) magneto-optical spectroscopy to investigate the cyclotron resonance in high mobility two-dimensional electron and hole systems. Our experiments reveal long-lived (~20 ps) coherent oscillations in the measured signal in the presence of a perpendicular magnetic field. The cyclotron frequency extracted from the oscillations varies linearly with magnetic field for a two-dimensional electron gas (2DEG), as expected. However, we find that the complex non-parabolic valence band structure in a two-dimensional hole gas (2DHG) causes the cyclotron frequency and effective mass to vary nonlinearly with the magnetic field, as verified by multiband Landau level calculations. This is the first time that THz magneto-optical spectroscopy has been used to study 2DHG, and we expect that these results will motivate further studies of these unique 2D nanosystems.Comment: 11 pages, 7 figure

Surface-Enhanced Nitrate Photolysis on Ice

Heterogeneous nitrates photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproducts quantum yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air/ice interface within the snowpack suppresses the diffusive uptake kinetics thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ~3-fold enhancement in photolysis rates to be correlated with the nitrates’ distorted intramolecular geometry thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than in the bulk. A simple 1D kinetic model suggests 1-that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO[subscript 2] emissions from a 5(8) nm thick photochemically active interfacial layer by 30%(60)%, and 2-that 25%(40%) of the NO[subscript 2] photochemical emissions to the snowpack interstitial air are released from the top-most molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface

Side-Mode-Suppression-Ratio οf Injection-Locked Fabry-Perot Lasers

The paper deals with numerical simulation and theoretical study of injection-locked Fabry-Perot semiconductor laser diodes and their transient and steady-state properties. Motivation for this research comes from the fact that Fabry-Perot semiconductor laser diodes seem to be good candidates for transmitters applied in optical network units of new generation wavelength-division-multiplexed passive optical networks. We base our model on the full scale multimode rate equation system, which comprises all supported longitudinal modes of Fabry-Perot semiconductor laser diode, providing its high reliability and broad applicability. We analyze the influence of bias current and spontaneous emission coupling factor on injection-locking characteristics of Fabry-Perot semiconductor laser diodes and find that injection power of the master laser required to maintain an acceptable side-mode-suppression-ratio strongly depends on these parameters. The emphasis of our investigation is on spontaneous emission coupling factor, since its value is often assumed rather than thoroughly calculated or measured. As we show in the paper, variations of this parameter may affect theoretical results and their comparison with experimental data

Superefficient electric-field–induced spin-orbit splitting in strained

We investigate theoretically the efficiency of the Rashba effect, i.e. the spin-orbit splitting resulting from an electric field. In contrast to previous studies, where the carriers have usually been taken to be electrons, we focus on holes and are able to demonstrate remarkable improvements of the effect by several orders of magnitude. We also show that the frequently-neglected lattice-mismatch between GaAs and AlGaAs can be used to further enhance the efficiency of the wave vector splitting mechanism. The Rashba effect is the fundamental mechanism behind the Datta-Das spin transistor and we find that for a small electric field of 2\un{kV/cm} the spin precession length becomes only 36\un{nm}

Phase Space of Tristability in Dual Injection-Locked Fabry-Perot Laser Diodes

We investigate theoretically the case of dual injection-locking, in which the two light signals are simultaneously externally injected into the cavity of a slave Fabry-Perot laser diode. We show that dual injection-locking leads to formation of new stationary points, and potentially to optical tristability of the slave laser. We show that a region in which the slave laser exhibits three stable steady-states occurs only for sufficiently different frequency detunings of the two injection signals. Moreover, the slave laser tunability depends on the choice of injection modes, and strongly depends on the slave laser bias current, with an optimal value around 2 times threshold current

Brix refractometry of colostrum from primiparous dairy cows and new-born calf blood serum in the evaluation of failure of passive transfer

Failure of passive transfer (FPT) of immunoglobulins (IgG) is associated with increased morbidity and mortality of calves. In this study we evaluated the digital Brix refractometer usefulness for the assessment of FPT. A number of 16 colostrum samples from the fi rst milking (2-3h post-partum) of Holstein-Friesian dairy heifers and 29 blood sera of 3-6 days old calves were analyzed with a digital Brix refractometer. Total proteins were determined by the biuret reaction. Colostral IgG were determined by radial immunodiffusion (RID), and colostral whey and blood serum ? globulin (composed almost entirely of IgG) were determined by agarose protein gel electrophoresis (APE) and densitometry. Colostral % Brix score was 25.5±3.4%. Concentrations of colostrum IgG and colostral whey ? globulin were 130±33 g/L and 100±24 g/L respectively. The concentration of total proteins in colostral whey was 134±30 g/L. The correlations between Brix values and the concentrations of IgG determined with RID and the concentrations of ? globulin determined with APE were positive and highly signifi cant (P<0.001 and P<0.01). The concentration of serum proteins of new-born calves was 57.75±11.8 g/L, the concentration of ? globulin was 14.4±7.8 g/L, and the Brix score was 8.6±1.0%. FPT (serum ? globulin<10 g/L) was detected in 34.5% (10/29) calves. Brix score correlated with the concentration of blood serum ? globulins in all examined calves. The results have confi rmed that digital Brix refractometry allows the producers to use this technique in order to estimate colostral and calf serum IgG, thereby monitoring both colostrum quality and success of passive transfer