A Simple Model for Magnetization Ratios in Doped Nanocrystals

Recent experiments on Mn-doped ZnS nanocrystals have shown unusual magnetization properties. We describe a nearest-neighbor Heisenberg exchange model for calculating the magnetization ratios of these antiferromagnetically doped crystals, in which the dopant atoms are distributed inhomogeneously within the nanocrystal. This simple inhomogeneous doping model is capable of reproducing the experimental results, and suggests that interior dopant atoms are localized within the crystal.Comment: 8 pages, 1 figure, 2 tables. Submitted to J. Appl. Phy

Atomistic Theory of Coherent Spin Transfer between Molecularly Bridged Quantum Dots

Time-resolved Faradary rotation experiments have demonstrated coherent transfer of electron spin between CdSe colloidal quantum dots coupled by conjugated molecules. We employ here a Green's function approach, using semi-empirical tight-binding to treat the nanocrystal Hamiltonian and Extended Huckel theory to treat the linking molecule Hamiltonian, to obtain the coherent transfer probabilities from atomistic calculations, without the introduction of any new parameters. Calculations on 1,4-dithiolbenzene and 1,4-dithiolcyclohexane linked nanocrystals agree qualitatively with experiment and provide support for a previous transfer Hamiltonian model. We find a striking dependence on the transfer probabilities as a function of nanocrystal surface site attachment and linking molecule conformation. Additionally, we predict quantum interference effects in the coherent transfer probabilities for 2,7-dithiolnaphthalene and 2,6-dithiolnaphthalene linking molecules. We suggest possible experiments based on these results that would test the coherent, through-molecule transfer mechanism.Comment: 12 pages, 9 figures. Submitted Phys. Rev.

Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. <br><br> Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode

Factors determining renal response to water immersion in non-excretor cirrhotic patients

Factors determining renal response to water immersion in non-excretor cirrhotic patients. Non-excretor cirrhotic patients, defined by their inability to normally excrete a standard water load, display variable responses to head–out water immersion. The hemodynamic, hormonal, and renal functional status of fifteen such patients were analyzed relative to water excretion during head-out water immersion. Group 1 patients (N = 7) all excreted less than 40% of the water load during immersion, whereas excretion was greater than 40% in all eight patients in Group 2. Group 1 patients, when compared with Group 2, had more ascites, more diuretic resistance, lower serum sodium concentration (125 ± 2 vs. 130 ± 1 mEq/liter, P < 0.05), and more impaired baseline water excretion (12.9 ± 1.2 vs. 35.9 ± 5.9% of water load in 5 hr, P < 0.005). Systemic hemodynamic responses to water immersion were similar in both groups. Glomerular filtration rate and renal plasma flow were significantly more impaired in Group 1 patients (inulin clearance 28 ± 6 vs. 62 ± 9 ml/min/1.73m2, P < 0.05; para-aminohippurate clearance 212 ± 35 vs. 357 ± 37 ml/min, P < 0.05). Concentrations of plasma vasopressin (1.7 ± 0.5 vs. 0.8 ± 0.1 pg/ml, P < 0.05), renin (8.6 ± 1.7 vs. 3.8 ± 0.9 ng/ml/hr, P < 0.05), aldosterone (82 ± 14 vs. 39 ± 10 ng/dl, P < 0.05) and norepinephrine (1155 ± 183 vs. 603 ± 126 pg/ml, P < 0.05) were all significantly higher in Group 1 than Group 2 patients during water immersion. Thus, non-excretor cirrhotic patients are not homogenous and appear to comprise a spectrum with those patients in whom water excretion is most impaired, having tense ascites, diuretic resistance, lower serum sodium concentrations, more impaired renal function, and more marked abnormalities in the hormonal markers of decreased effective blood volume

Characterization of designed, synthetically accessible bryostatin analog HIV latency reversing agents.

HIV latency in resting CD4+ T cell represents a key barrier preventing cure of the infection with antiretroviral drugs alone. Latency reversing agents (LRAs) can activate HIV expression in latently infected cells, potentially leading to their elimination through virus-mediated cytopathic effects, host immune responses, and/or therapeutic strategies targeting cells actively expressing virus. We have recently described several structurally simplified analogs of the PKC modulator LRA bryostatin (termed bryologs) designed to improve synthetic accessibility, tolerability in vivo, and efficacy in inducing HIV latency reversal. Here we report the comparative performance of lead bryologs, including their effects in reducing cell surface expression of HIV entry receptors, inducing proinflammatory cytokines, inhibiting short-term HIV replication, and synergizing with histone deacetylase inhibitors to reverse HIV latency. These data provide unique insights into structure-function relationships between A- and B-ring bryolog modifications and activities in primary cells, and suggest that bryologs represent promising leads for preclinical advancement

Norepinephrine-induced acute renal failure: A reversible ischemic model of acute renal failure

Several studies have shown that acute renal failure (ARF) can be produced in the dog by infusing norepinephrine (NE) into a renal artery [1, 2]. In these studies the injury appeared to be confined to the infused kidney, with no changes occurring in systemic hemodynamics or in the function of the contralateral kidney. The hemodynamic changes noted in the infused kidney were comparable to those seen in human ARF. A major criticism of these studies, however, is that the renal failure was not shown to be reversible, as it typically is in man. In the present study, we have reexamined the NE-induced model of ARF in the dog with the particular purpose of finding a set condition which would cause ARF and yet allow recovery of renal function within a period of time comparable to that usually seen in the human disease

Evaluation of the EndoPAT as a Tool to Assess Endothelial Function

Endothelial dysfunction is a potential target for (pharmaceutical) intervention of several systemic pathological conditions. We investigated the feasibility of the EndoPAT to evaluate acute changes in endothelial function with repeated noninvasive measurements and assessed its discriminating power in different populations. Endothelial function was stable over a longer period of time in renally impaired patients (coefficient of variation 13%). Endothelial function in renally impaired and type 2 diabetic patients was not decreased compared to healthy volunteers (2.9 ± 1.4 and 1.8 ± 0.3, resp., versus 1.8 ± 0.5, P > 0.05). The EndoPAT did not detect an effect of robust interventions on endothelial function in healthy volunteers (glucose load: change from baseline 0.08 ± 0.50, 95% confidence interval −0.44 to 0.60; smoking: change from baseline 0.49 ± 0.92, 95% confidence interval −0.47 to 1.46). This suggests that at present the EndoPAT might not be suitable to assess (changes in) endothelial function in early-phase clinical pharmacology studies. Endothelial function as measured by the EndoPAT could be physiologically different from endothelial function as measured by conventional techniques. This should be investigated carefully before the EndoPAT can be considered a useful tool in drug development or clinical practice