Irreversible magnetization switching using surface acoustic waves

An analytical and numerical approach is developped to pinpoint the optimal experimental conditions to irreversibly switch magnetization using surface acoustic waves (SAWs). The layers are magnetized perpendicular to the plane and two switching mechanisms are considered. In precessional switching, a small in-plane field initially tilts the magnetization and the passage of the SAW modifies the magnetic anisotropy parameters through inverse magneto-striction, which triggers precession, and eventually reversal. Using the micromagnetic parameters of a fully characterized layer of the magnetic semiconductor (Ga,Mn)(As,P), we then show that there is a large window of accessible experimental conditions (SAW amplitude/wave-vector, field amplitude/orientation) allowing irreversible switching. As this is a resonant process, the influence of the detuning of the SAW frequency to the magnetic system's eigenfrequency is also explored. Finally, another - non-resonant - switching mechanism is briefly contemplated, and found to be applicable to (Ga,Mn)(As,P): SAW-assisted domain nucleation. In this case, a small perpendicular field is applied opposite the initial magnetization and the passage of the SAW lowers the domain nucleation barrier.Comment: 11 pages, 4 figure

Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach

Using an advanced tight-binding approach, we estimate the anisotropy of the tunnel transmission associated with the rotation of the 5/2 spin of a single Mn atom forming an acceptor state in GaAs and located near an AlGaAs tunnel barrier. Significant anisotropies in both in-plane and out-of-plane geometries are found, resulting from the combination of the large spin-orbit coupling associated with the p-d exchange interaction, cubic anisotropy of heavy-hole dispersion and the low C2v symmetry of the chemical bonds.Comment: 4 pages, 3 figure

MRI-DTI Imaging Reveals Specific Neuro-degeneration Signature in Precuneus Node of Awareness Processing in Brain under Alzheimer’s Disease

Introduction:Alzheimer's disease(AD) displays progressive neurodegenerative atrophy, causing neuronal lossaffecting cognitive skills and memory. As precuneus is associated with episodic memory and is the reflexive self-awareness hub node, we consider precuneus as region-of-interest(ROI) for analysing AD.Objective:The main objective is find AD-caused alteration in nerve fibres, using diffusion tensor imaging(DTI) parameters like Mean Diffusivity(MD), Fractional Anisotropy(FA), and Nerve-tract Parameters, as number, length, volume, density, and thus, analyse the effect on precuneus by AD [when compared to normal subjects(CN)].Materials/Methods:Normals and Alzheimer’s subjects (n=50 each) were scanned with Siemens 3-tesla MRI-scanner. DTI parameters were estimated by DSI-FSL procedure, with statistical analysis usingt-test/ANOVA.Results:While ageing-process occurs in both AD and CN subjects, there is no change in “macro-structural” nerve fibre characteristics (e.g. Tract Indices: Number, density, volume, length). Contrastingly, there is significant alteration in “micro-structural” fibre characteristics, as increase in Mean Diffusivity(p=0.0006) and decrease in Fractional Anisotropy(p=0.0009) in Alzheimer's disease, when compared with normal subjects. Furthermore, comparing left-versus-right brain, Alzheimer’s patients (but not Normal subjects) show diminution in macro-structural nerve characteristics in left precuneus (compared to right precuneus): namely Tract’s number(p=0.0010), length(p=0.0107), volume(p=0.0225), density(p=0.0340).Conclusion:Under neurodegeneration, change in “micro-structural” nerve-fibre characteristics (Tract Indices), as opposed to “macro structural” fibre indices, can be hallmark for AD. Moreover, right precuneus is more protected in AD. Conversely, left precuneus has more neurodegeneration since its blood-flow is supplied by left common-carotid artery (unlike right common-carotid artery), this left artery arises directly from high-pressure aortic flow, transmitting turbulent hemodynamic stress to left precuneus

Formulation and evaluation of xanthan gum based aceclofenac tablets for colon targeted drug delivery

The objective of the present study is to develop a colon targeted drug delivery systems for Aceclofenac using xanthan gum as a carrier. In this study, multilayer coated system that is resistant to gastric and small intestinal conditions but can be easily degraded by colonic bacterial enzymes was designed to achieve effective colon delivery of Aceclofenac. The xanthan gum, the drug and the physical mixture were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). All the formulations were evaluated for hardness, drug content uniformity and other physical properties. Release aspects of Aceclofenac in simulated gastrointestinal fluid and colonic fluid with enzymes were investigated. From these results, Eudragit coated system exhibited gastric and small intestinal resistance to the release of Aceclofenac. The rapid increase in release of Aceclofenac in SCF was revealed as due to the degradation of the xanthan gum membrane by bacterial enzymes. The designed system could be used potentially as a carrier for colon delivery of Aceclofenac by regulating drug release in stomach and the small intestine.<br>O presente estudo teve como objetivo o desenvolvimento de sistema de liberação cólon-alvo de aceclofenaco empregando goma xantana. Nesse trabalho, o revestimento de múltiplas camadas com característica de resistência às condições do intestino delgado além de gastrorresistência oferece como vantagem a rápida degradação desse sistema por enzimas bacterianas colônicas. Dessa forma, o planejamento de tal sistema possibilitou a liberação específica do aceclofenaco no cólon. A goma xantana e o fármaco, além da mistura física desses dois componentes, foram caracterizados por espectroscopia no infravermelho com transformada de Fourier (FTIR) e calorimetria diferencial exploratória (DSC). Todas as formulações foram avaliadas no que se refere à dureza, à uniformidade de conteúdo do fármaco além de outras propriedades físicas. Os perfis de liberação do aceclofenaco no fluido gástrico simulado e fluido colônico simulado contendo enzimas foram investigados. Os resultados revelaram que o sistema revestido com Eudragit® exibiu resistência gástrica e intestinal à liberação de aceclofenaco. O rápido aumento na liberação de aceclofenaco no fluido colônico simulado foi atribuido à degradação da goma xantana por enzimas bacterianas. O sistema apresenta aplicação potencial no desenvolvimento de produtos para a liberação cólon-alvo de aceclofenaco

HLA-DQA1 & DQB1 variants associated with hepatitis B virus-related chronic hepatitis, cirrhosis & hepatocellular carcinoma

Background & objectives: Clinical outcome after hepatitis B virus (HBV) exposure varies extremely from spontaneous clearance to chronic hepatitis B and often progresses to liver cirrhosis (LC) and hepatocellular carcinoma (HCC). Host genetic factor plays an important role in the regulation of immune response. This study was aimed to investigate whether HLA class II DQA1 and DQB1 gene polymorphism were associated with chronic hepatitis B infection and in the development of HBV-related LC and HCC. Methods: DQA1 and DQB1 allele polymorphism were studied in 187 patients with HBV-related liver diseases (which included 73 chronic hepatitis B, 84 LC and 30 HCC patients) and 109 controls who had spontaneously recovered from HBV infection using polymerase chain reaction amplification with sequence-specific primers. Results: Our data suggested that DQA1*0101/2/4 [odds ratio (OR)=2.78; Pc=0.003], DQA1*0103 (OR=2.64; Pc=0.0007) and DQB1*0302/3 (OR=2.15; Pc=0.01) were associated with the protection from chronic HBV infection, whereas DQB1*0402 (OR=0.25; Pc=0.001) showed susceptible effect on chronic HBV infection. DQB1*0601 (OR=3.73; Pc=0.006) conferred protective effect from developing LC; similarly, DQB1*0302/3 (OR=5.53; Pc=0.05) and DQB1*0402 (OR=0.00; Pc=0.001) conferred protective effect from developing HCC. However, DQA1*0601 and DQB1*0503 showed susceptible effect on chronic HBV infection; these associations were no longer significant after Bonferroni correction. Interpretation & conclusions: Our results revealed HLA-DQA1*0101/2/4 - DQA1*0103 - DQB1*0302/3 and DQB1*0601 as protective and DQB1*0402 as risk alleles. The study suggests that various subtypes of HLA-DQA1 and DQB1 are associated with both HBV clearance and development of chronic HBV infections