Dynamics of a Pair of Interacting Spins Coupled to an Environmental Sea

We solve for the dynamics of a pair of spins, coupled to each other and also to an environmental sea of oscillators. The environment mediates an indirect interaction between the spins, causing both mutual coherence effects and dissipation. This model describes a wide variety of physical systems, ranging from 2 coupled microscopic systems (eg., magnetic impurities, bromophores, etc), to 2 coupled macroscopic quantum systems. We obtain analytic results for 3 regimes, viz., (i) The locked regime, where the 2 spins lock together; (ii) The correlated relaxation regime (mutually correlated incoherent relaxation); and (iii) The mutual coherence regime, with correlated damped oscillations. These results cover most of the parameter space of the system.Comment: 49 pages, To appear in Int J. Mod. Phys.

Broadband, unpolarized repumping and clearout light sources for Sr+^+ single-ion clocks

Future transportable optical clocks require compact and reliable light sources. Here, broadband, unpolarized repumper and state clearout sources for Sr+ single-ion optical clocks are reported. These turn-key devices require no frequency stabilization nor external modulators. They are fiber based, inexpensive, and compact. Key characteristics for clock operation are presented, including optical spectra, induced light shifts and required extinction ratios. Tests with an operating single-ion standard show a clearout efficiency of 100%. Compared to a laser-based repumper, the achievable fluorescence rates for ion detection are a few tens of per cent lower. The resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the ion system. Similar repumper light sources could be made for Ca+ (866 nm) and Ba+ (650 nm) using semiconductor gain media.Comment: 4 pages, 6 figure

Different models and single-nucleotide polymorphisms signal the simulated weak gene-gene interaction for a quantitative trait using haplotype-based and mixed models testing

Knowledge of simulated genetic effects facilitates interpretation of methodological studies. Genetic interactions for common disorders are likely numerous and weak. Using the 200 replicates of the Genetic Analysis Workshop 16 (GAW16) Problem 3 simulated data, we compared the statistical power to detect weak gene-gene interactions using a haplotype-based test in the UNPHASED software with genotypic mixed model (GMM) and additive mixed model (AMM) mixed linear regression model in SAS. We assumed a candidate-gene approach where a single-nucleotide polymorphism (SNP) in one gene is fixed and multiple SNPs are at the second gene. We analyzed the quantitative low-density lipoprotein trait (heritability 0.7%), modulated by simulated interaction of rs4648068 from 4q24 and another gene on 8p22, where we analyzed seven SNPs. We generally observed low power calculated per SNP (≤ 37% at the 0.05 level), with the haplotype-based test being inferior. Over all tests, the haplotype-based test performed within chance, while GMM and AMM had low power (~10%). The haplotype-based and mixed models detected signals at different SNPs. The haplotype-based test detected a signal in 50 unique replicates; GMM and AMM featured both shared and distinct SNPs and replicates (65 replicates shared, 41 GMM, 27 AMM). Overall, the statistical signal for the weak gene-gene interaction appears sensitive to the sample structure of the replicates. We conclude that using more than one statistical approach may increase power to detect such signals in studies with limited number of loci such as replications. There were no results significant at the conservative 10-7 genome-wide level

Influence of wind on crop canopy reflectance measurements

Remote sensing techniques of measuring red and far-red crop canopy reflectance are frequently used to estimate crop canopy characteristics. The variability introduced in reflectance data from nonvegetative factors such as wind decreases the usefulness of the techniques. The objective of this study was to quantify and minimize the variability from wind on spectral reflectances. Red and far-red reflectances were acquired above wheat, barley, and alfalfa canopies throughout days of changing wind conditions. Periods of 312 s with little changes in irradiance values were used for the analysis. Wind had negligible effect on reflectances of a short canopy such as cut alfalfa, while it had a significant effect on reflectances from canopies with a higher vertical structure, particularly during gusty conditions. Within the windy and calm periods, extreme values of spectral reflectance differed by 60% and 12%, respectively, in the red, and by 40% and 8% in the far-red for the barley canopy. For the compact and dense canopy structure of alfalfa, these differences reached a maximum of 10% under windy conditions in both spectral regions. The plant canopy architecture, the wind conditions, and the spectral regions all affected the magnitude of the influence of wind on crop canopy spectral reflectances. The mean reflectance of a canopy overestimated the true reflectance by 2–4% while the use of the median reduced this overestimation. Sampling requirements for this sensor are evaluated, and the possibility of decreasing either the sampling rate or the sampling period is discussed

Sun-angle effects on the red and near infrared reflectances of five different crop canopies

The objective of this paper is to study relationships between dai/y variations in sun angles and red and near infrared reflectances measured throughout a growing season over different types of crop canopies. Five architecturally different crop canopies were planted: wheat (NNW-SSE rows 0.18 m and 0.35 m apart), barley (NNW-SSE rows 0.18 m apart), corn (NNWSSE rows 0.46 m apart), and sunflower (N-S rows 0.92 m apart). Each canopy was planted at three different densifies in order to add intraspecies variability. Spectral reflectances were measured with a sensor in the nadir position located on a ground platform. Changes in sun angles usually affected the red more than near infrared reflectances. Within each crop, the canopies with the lowest LAI a/ways showed the larges! variations in spectral reflectances. But among the crops, the importance of changing sun angles on crop canopy reflectances varied with the architecture of the canopy. Red reflectances collected over corn and sunflower at LAI of 6 were insensitive to changes in sun angles, while those collected above sunflower showed significant differences when LAI was around 4. The higher proportion of horizontal foliar area compared to the vertical one in corn canopies could account for this difference between the two crops, since a canopy with horizontal foliar distribution is a nearer approximation of a lambertian surface. The differences in row width and orientation could also explain some of these differences. Reflectances of wheat canopies planted with rows 0.35 m apart showed larger red reflectance variations within a day than those planted 0.17 m apart. The maximum red reflectances always appeared when the sun was in fine with row direction. The fact that most rapid variations in red reflectances were occurring around this particular time of the day also confirmed that there is a strong interaction between row direction and width with the position of the sun in the sky. The magnitude of the effect of the variations of sun angles on crop canopy spectral reflectances was shown to be dependent on the species, planting patterns, wavelength band, and sky conditions. Le présent article décrit une étude des relations entre les variations quotidiennes de l'angle du soleil ainsi que des réflectances dans le rouge et le proche infrarouge mesurées tout au long d'une saison de récolte sur différents types de couverts végétaux. Cinq couverts végétaux de structure différente ont été semés: blé (rangs NNO-SSE à intervalles de 0,18 et 0,35 mètres), orge (rangs NNO-SSE à intervalles de 0,18 mètre), maïs (rangs NNO-SSE à intervalles de 0,46 mètre) et tournesol (rangs N-S à intervalles de 0,92 mètre). Chaque couvert végétal a été semé à trois densités différentes de manière à pouvoir mesurer la variabilité au sein de chaque espèce. Les réflectances spectrales ont été mesurées à la position nadir à l'aide d'un capteur fixé à une plate-forme au sol. En général, les variations de l'angle du soleil touchaient davantage les réflectances dans le rouge que les réflectances dans le proche infrarouge. Pour chaque culture, les couverts ayant l'indice de surface foliaire (ISF) le moins élevé ont systématiquement donné la plus grande variation au niveau des réflectances spectrales. Par contre, entre les diverses cultures, la variation de l'angle du soleil sur les réflectances des couverts végétaux était fonction de la structure du couvert. Les réflectances rouges recueillies au-dessus du maïs et du tournesol avec un ISF de 6 étaient insensibles aux variations de l'angle du soleil, tandis que celles mesurées au-dessus des tournesols variaient substantiellement lorsque l'ISF était aux environs de 4. Cette différence entre les deux cultures peut s'expliquer par la présence d'une plus grande distribution foliaire horizontale comparativement à la surface verticale offerte par le couvert de maïs, puisqu'un couvert ayant une distribution foliaire horizontale se rapproche davantage d'une surface lambertienne. La différence dans la largeur et l'orientation des rangs pourrait aussi expliquer certaines de ces différences. Les couverts de blé semés en rangs à intervalles de 0,35 mètre ont donné des variations de réflectances dans le rouge plus grandes dans une journée que ceux semés à intervalles de 0,17 mètre. Les réflectances maximales dans le rouge se produisaient toujours lorsque le soleil était en ligne avec les rangs. Le fait que la plupart des variations rapides des réflectances dans le rouge se produisaient à ce moment particulier de la journée a aussi confirmé qu'il existe une forte corrélation entre la direction et la largeur des rangs et la position du soleil dans le ciel. Cette étude a démontré que l'ampleur de l'incidence des variations de l'angle du soleil sur les réflectances spectrales des couverts végétaux est fonction de l'espèce, du mode de semence, de la longueur d'ondes de la bande et des conditions du ciel

Cavity ring-down spectroscopy instrumentation for airborne detection of nitrogen oxides

Pulsed laser cavity ring-down spectroscopy (CaRDS) is a highly sensitive method for direct absorption spectroscopy that has been applied to in-situ detection of NO3, N2O5, NO2, NO, and O3, as well as NOx and NOy in the atmosphere from a variety of airborne platforms. CaRDS instruments have traditionally been large and delicate laboratory instruments. The successful leap from laboratory instruments with high maintenance requirements to compact and rugged field instruments for airborne deployment was made possible through the extensive engineering work and new innovations presented in this thesis. The necessary improvements were mainly in the six following areas: 1) Instrument rack design and vibration isolation, 2) Automated aerosol filter changer, 3) Low loss inlet design and flow control, 4) Optical cage design, 5) Clamped/nudged mirror mount, and 6) Purge system improvements. The result was a series of compact, reliable, and rugged field instruments with high sensitivity and accuracy. The first airborne deployment was performed in 2004. The designs have been copied by several other research groups, and airborne measurements with CaRDS instruments are now considered routine

Dexamethasone Attenuates Hyperexcitability Provoked by Experimental Febrile Status Epilepticus.

The role of neuroinflammation in the mechanisms of epilepsy development is important because inflammatory mediators provide tractable targets for intervention. Inflammation is intrinsically involved in the generation of childhood febrile seizures (FSs), and prolonged FS [febrile status epilepticus (FSE)] precedes a large proportion of adult cases of temporal lobe epilepsy (TLE). As TLE is often refractory to therapy and is associated with serious cognitive and emotional problems, we investigated whether its development can be prevented using anti-inflammatory strategies. Using an immature rat model of FSE [experimental FSE (eFSE)], we administered dexamethasone (DEX), a broad anti-inflammatory agent, over 3 d following eFSE. We assessed eFSE-provoked hippocampal network hyperexcitability by quantifying the presence, frequency, and duration of hippocampal spike series, as these precede and herald the development of TLE-like epilepsy. We tested whether eFSE provoked hippocampal microgliosis, astrocytosis, and proinflammatory cytokine production in male and female rats and investigated blood-brain barrier (BBB) breaches as a potential contributor. We then evaluated whether DEX attenuated these eFSE sequelae. Spike series were not observed in control rats given vehicle or DEX, but occurred in 41.6% of eFSE-vehicle rats, associated with BBB leakage and elevated hippocampal cytokines. eFSE did not induce astrocytosis or microgliosis but provoked BBB disruption in 60% of animals. DEX significantly reduced spike series prevalence (to 7.6%) and frequency, and abrogated eFSE-induced cytokine production and BBB leakage (to 20%). These findings suggest that a short, postinsult intervention with a clinically available anti-inflammatory agent potently attenuates epilepsy-predicting hippocampal hyperexcitability, potentially by minimizing BBB disruption and related neuroinflammation

Randomized Controlled Trial of an Internet Application to Reduce HIV Transmission Behavior Among HIV Infected Men Who have Sex with Men.

We conducted a prospective, randomized controlled trial of an internet-based safer-sex intervention to reduce HIV transmission risk behaviors. HIV-infected men who have sex with men (n = 179) were randomized to receive a monthly internet survey alone or a monthly survey plus tailored risk reduction messages over 12 months. The primary outcome was the cumulative sexually transmitted infection (STI) incidence over 12 months. Secondary outcomes included self-reported unprotected sex with an at risk partner and disclosure of HIV status to partners. In a modified intent to treat analysis, there was no difference in 12-month STI incidence between the intervention and control arms (30 vs. 25 %, respectively; p = 0.5). Unprotected sex decreased and disclosure increased over time in both study arms. These improvements suggest that addition of the risk-reduction messages provided little benefit beyond the self-monitoring of risky behavior via regular self-report risk behavior assessments (as was done in both study arms)

Lithium-ion battery aging experiments at subzero temperatures and model development for capacity fade estimation

Lithium-ion (Li-ion) batteries widely used in electric vehicles (EVs) and hybrid EVs (HEVs) are insufficient for vehicle use after they have degraded to 70% to 80% of their original capacity. Battery lifespan is a large consideration when designing battery packs for EVs/HEVs. Aging mechanisms, such as metal dissolution, growth of the passivated surface film layer on the electrodes, and loss of both recyclable lithium ions, affect the longevity of the Li-ion battery at higherature operations. Even vehicle maneuvers at low temperatures (T<0°C)contribute to battery lifetime degradation, owing to the anode electrode vulnerability to other degradation mechanisms such as lithium plating. Nowadays, only a few battery thermal management schemes have properly considered lowerature degradation. This is due to the lack of studies on aging of Li-ion batteries at sub-zero temperature. This paper investigates how load cycle and calendar life properties affect the lifetime and aging processes of Li-ion cells at low temperatures. Accelerated aging tests were used to determine the effect of the ambient temperature on the performance of three 100-Ah LiFeMnP04 Li-ion cells. Two of them were aged through a normalized driving cycle at two temperature tests (-20°C and 25°C). The calendar test was carried out on one single battery at -20 °C and mid-range of state of charge (50%). Their capacities were continuously measured every two or three days. An aging model is developed and added to a preliminary single-cell electrothermal model to establish, in future works, a thermal strategy capable of predicting how the cell ages. This aging model was then validated by comparing its predictions with the aging data obtained from a cycling test at 0 °C. © 1967-2012 IEEE

Applying the Functional Behavioral and Social Sciences Research (BSSR) Framework to HIV Cure Research

Introduction The search for an HIV cure involves important behavioural and social processes that complement the domains of biomedicine. However, the field has yet to tap into the full potential of behavioural and social sciences research (BSSR). In this article, we apply Gaist and Stirratt’s BSSR Functional Framework to the field of HIV cure research. Discussion The BSSR Functional Framework describes four key research domains: (1) basic BSSR (understanding basic behavioural and social factors), (2) elemental BSSR (advancing behavioural and social interventions), (3) supportive BSSR (strengthening biomedically focused clinical trials), and (4) integrative BSSR (building multi-disciplinary combination approaches for real-world implementation). In revisiting and applying the BSSR Functional Framework, we clarify the importance of BSSR in HIV cure research by drawing attention to such things as: how language and communication affect the meaning of “cure” to people living with HIV (PLHIV) and broader communities; how cure affects the identity and social position of PLHIV; counselling and support interventions to address the psychosocial needs and concerns of study participants related to analytical treatment interruptions (ATIs); risk reduction in the course of ATI study participation; motivation, acceptability, and decision-making processes of potential study participants related to different cure strategies; HIV care providers’ perceptions and attitudes about their patients’ participation in cure research; potential social harms or adverse social events associated with cure research participation; and the scalability of a proven cure strategy in the context of further advances in HIV prevention and treatment. We also discuss the BSSR Functional Framework in the context of ATIs, which involve processes at the confluence of the BSSR domains. Conclusions To move HIV cure regimens through the translational research pathway, attention will need to be paid to both biomedical and socio-behavioural elements. BSSR can contribute an improved understanding of the human and social dimensions related to HIV cure research and the eventual application of HIV cure regimens. The BSSR Functional Framework provides a way to identify advances, gaps and opportunities to craft an integrated, multi-disciplinary approach at all stages of cure research to ensure the real-world applicability of any strategy that shows promise