Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $\delta$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $\delta$ can become negative.Comment: 11 pages, 2 eps figure

Indirect exchange in GaMnAs bilayers via spin-polarized inhomogeneous hole gas: Monte Carlo simulation

The magnetic order resulting from an indirect exchange between magnetic moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs double layer structure is studied via Monte Carlo simulation. The coupling mechanism involves a perturbative calculation in second order of the interaction between the magnetic moments and carriers (holes). We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layers, establishing, in this way, a self-consistency between the magnetic order and the electronic structure. That interaction leads to an internal ferromagnetic order inside each layer, and a parallel arrangement between their magnetizations, even in the case of thin layers. This fact is analyzed in terms of the inter- and intra-layer interactions.Comment: 17 pages and 14 figure

Post-Transcriptional Dysregulation by miRNAs Is Implicated in the Pathogenesis of Gastrointestinal Stromal Tumor [GIST]

peer-reviewedIn contrast to adult mutant gastrointestinal stromal tumors [GISTs], pediatric/wild-type GISTs remain poorly understood overall, given their lack of oncogenic activating tyrosine kinase mutations. These GISTs, with a predilection for gastric origin in female patients, show limited response to therapy with tyrosine kinase inhibitors and generally pursue a more indolent course, but still may prove fatal. Defective cellular respiration appears to underpin tumor development in these wild-type cases, which as a group lack expression of succinate dehydrogenase [SDH] B, a surrogate marker for respiratory chain metabolism. Yet, only a small subset of the wild-type tumors show mutations in the genes coding for the SDH subunits [SDHx]. To explore additional pathogenetic mechanisms in these wild-type GISTs, we elected to investigate posttranscriptional regulation of these tumors by conducting microRNA (miRNA) profiling of a mixed cohort of 73 cases including 18 gastric pediatric wild-type, 25 (20 gastric, 4 small bowel and 1 retroperitoneal) adult wild-type GISTs and 30 gastric adult mutant GISTs. By this approach we have identified distinct signatures for GIST subtypes which correlate tightly with clinico-pathological parameters. A cluster of miRNAs on 14q32 show strikingly different expression patterns amongst GISTs, a finding which appears to be explained at least in part by differential allelic methylation of this imprinted region. Small bowel and retroperitoneal wild-type GISTs segregate with adult mutant GISTs and express SDHB, while adult wildtype gastric GISTs are dispersed amongst adult mutant and pediatric wild-type cases, clustering in this situation on the basis of SDHB expression. Interestingly, global methylation analysis has recently similarly demonstrated that these wild-type, SDHB-immunonegative tumors show a distinct pattern compared with KIT and PDGFRA mutant tumors, which as a rule do express SDHB. All cases with Carney triad within our cohort cluster together tightly.Funding was obtained from the Medical Research Charities Group (http://www.mrcg.ie/) and Health Research Board of Ireland (http://www.hrb.ie) (MO’S), The Children’s Medical and Research Foundation (http://www.cmrf.org) (MO’S), the GIST Cancer Awareness Foundation [GCAF] (http://www. gistawareness.org/)(MO’S), and research grants from the Life Raft Group (http://www.liferaftgroup.org/)(MD-R) and from the Fonds voor Wetenschappelijk Onderzoek Vlaanderen (http://www.fwo.be/)(grant # G.0286.05 MD-R)

Spin flip scattering in magnetic junctions

Processes which flip the spin of an electron tunneling in a junction made up of magnetic electrodes are studied. It is found that: i) Magnetic impurities give a contribution which increases the resistance and lowers the magnetoresistance, which saturates at low temperatures. The conductance increases at high fields. ii) Magnon assisted tunneling reduces the magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons, which may appear if the interface has different magnetic properties from the bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and resistance, respectively, and, iv) Coulomb blockade effects may enhance the magnetoresistance, when transport is dominated by cotunneling processes.Comment: 5 page

Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter

Phase II Study of Sequential Gemcitabine Followed by Docetaxel for Recurrent Ewing Sarcoma, Osteosarcoma, or Unresectable or Locally Recurrent Chondrosarcoma: Results of Sarcoma Alliance for Research Through Collaboration Study 003

Background.Gemcitabine and docetaxel have a broad spectrum of clinical activity in patients with carcinoma. The Sarcoma Alliance for Research Through Collaboration conducted a phase II trial of gemcitabine in combination with docetaxel in children and adults with recurrent Ewing sarcoma (EWS), osteosarcoma (OS), or unresectable or recurrent chondrosarcoma. The primary objective was to determine the objective response rate using Response Evaluation Criteria in Solid Tumors (RECIST).Methods.Gemcitabine (675 mg/m2 i.v. over 90 minutes on days 1 and 8) was administered in combination with docetaxel (75 mg/m2 i.v. over 1 hour on day 8) every 21 days. All patients received filgrastim or pegfilgrastim. A Bayesian formulation was used to determine the probability of achieving the target response rate for each subtype—0.35 for EWS and OS or 0.20 for chondrosarcoma. If the probability of achieving the target response rate was <0.05, the combination was considered inactive. Toxicity was graded according to Common Terminology Criteria for Adverse Events (CTCAE), version 3.0.Results.Fifty‐three eligible patients were enrolled in the three subtype groups—OS (n = 14), EWS (n = 14), and chondrosarcoma (n = 25). Toxicities included neutropenia, thrombocytopenia, fatigue, dyspnea, bronchospasm, edema, neuropathy, and liver function abnormalities. Dose modification for toxicity was required for eight patients during cycle 1 and 16 patients in subsequent cycles. Seven patients withdrew from therapy as a result of toxicity. No complete responses were observed. Partial responses were observed in OS (n = 1), EWS (n = 2), and chondrosarcoma (n = 2) patients.Conclusion.Gemcitabine in combination with docetaxel was associated with a probability of reaching the target 35% response rate of <5% in OS patients and 5.6% in EWS patients; the probability of reaching a 20% response rate in chondrosarcoma patients was 14%.摘要背景. 吉西他滨与多西他赛对癌症患者有广谱的临床疗效。 肉瘤研究联盟协作组在复发的尤文肉瘤 （EWS）、 骨肉瘤 （OS）、 不可切除或复发的软骨肉瘤成人和儿童患者中开展了吉西他滨联合多西他赛的 II 期试验。 主要目的为通过实体瘤疗效评估标准 （RECIST） 确定客观缓解率。方法. 吉西他滨 （675 mg/m2， 静脉滴注 90 分钟以上， 第 1 和 8 天） 联合多西他赛 （75 mg/m2， 静脉滴注 1 小时以上， 第 8 天） 每 21 天给药 1 次。 全部患者均同时接受非格司亭或乙二醇化非格司亭。 利用贝叶斯公式来确定各个亚型达到目标缓解率的概率——EWS 和 OS 为 0.35， 软骨肉瘤为 0.20。 如果达到目标缓解率的概率 < 0.05， 则认为联合方案无效。 毒性反应根据不良事件通用术语标准 （CTCAE） 3.0 版来分级。结果. 53 例合格患者入组 3 个亚型组 ： OS （n=14）、 EWS （n=14）、 软骨肉瘤 （n=25）。 毒性反应包括中性粒细胞减少、 血小板减少、 乏力、 呼吸困难、 支气管痉挛、 水肿、 神经病变以及肝功能异常。 第 1 个周期有 8 例患者、 其后周期有 16 例患者因毒性反应而需要剂量调整。 7 例患者因毒性反应而撤出治疗。 未观察到完全缓解。 OS （n=1）、 EWS （n=2） 和软骨肉瘤 （n=2） 组均有患者达到部分缓解。结论. 吉西他滨联合多西他赛在 < 5% 的 OS 患者、 5.6% 的 EWS 患者中达到目标缓解率的概率为 35%； 14% 软骨肉瘤患者中达到目标缓解率的概率为 20%。讨论. 贝叶斯公式能够评估各个亚型在分别进行缓解率评估后预测达到目标缓解率的概率。 通过多角度来看这些数据， 在考量达到目标缓解率的概率以及入组率之后即能发现本研究设计方案阻碍了研究的继续开展。 因为这一设计方案并未设定判断治疗为 “有效” 的规则， 所以并不适合与标准的分 2 阶段进行的 II 期试验设计直接比较。 关闭 EWS 和软骨肉瘤亚组的决定， 某种程度上是基于入组缓慢， 另外达到目标缓解率的概率较低也支持这一决定。 入组率而不是统计设计， 对试验周期有显著影响。The Oncologist 2012;17:321‐e329Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139909/1/onco0321-sup-0002.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139909/2/onco0321-sup-0001.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139909/3/onco0321.pd

Bulk Mediated Surface Diffusion: Non Markovian Desorption with Finite First Moment

Here we address a fundamental issue in surface physics: the dynamics of adsorbed molecules. We study this problem when the particle's desorption is characterized by a non Markovian process, while the particle's adsorption and its motion in the bulk are governed by a Markovian dynamics. We study the diffusion of particles in a semi-infinite cubic lattice, and focus on the effective diffusion process at the interface $z = 1$. We calculate analytically the conditional probability to find the particle on the $z=1$ plane as well as the surface dispersion as functions of time. The comparison of these results with Monte Carlo simulations show an excellent agreement.Comment: 16 pages, 7 figs. European Physical Journal B (in press

Nanosized Sodium-Doped Lanthanum Manganites: Role of the Synthetic Route on their Physical Properties

In this paper we present the results of the synthesis and characterisation of nanocrystalline La1-xNaxMnO3+delta samples. Two synthetic routes were employed: polyacrylamide-based sol-gel and propellant synthesis. Pure, single phase materials were obtained with grain size around 35 nm for the sol-gel samples and around 55 nm for the propellant ones, which moreover present a more broaden grain size distribution. For both series a superparamagnetic behaviour was evidenced by means of magnetisation and EPR measurements with peculiar features ascribable to the different grain sizes and morphology. Preliminary magnetoresistivity measurements show enhanced low-field (< 1 T) magnetoresistance values which suggest an interesting applicative use of these manganites.Comment: 31 Pages 10 Figures to appear in Chem. Mate