Nanorod heterostructures showing photoinduced charge separation

Size- and shape-dependent property modifications of semiconductor nanocrystals have been a subject of intense interest because of their potential for future engineering devices. The bandgap and related optical-property tuning of these materials are mainly governed by the nature of their band edges. In addition, fusing one type of nanocrystal over another enables further control of material properties that are dependent on the relative alignments of their energy levels. On a molecular scale, the synthesis of supramolecular compounds has inspired advances in theories for photoinduced charge transfer. Heterostructured nanocrystals potentially provide a nanoscale analog of such systems. A method for preparing heterostructured nanocrystals of complex morphologies showing photoinduced charge separation is presented. It is shown that the energy and lifetime of the charge-transfer photoluminescence band can be tuned by changing the relative alignment of band edges in CdSe/CdTe heterostructure nanorods. The long-lived charge transfer states in these type II semiconductors may make them attractive for photovoltaic applications.     

Deposition of tellurium films by decomposition of electrochemically-generated H2Te: application to radiative cooling devices

The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H₂Te. Pre-treatment of the polyethylene substrates with KMnO₄ to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H₂Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.     

An assessment of stress intensity factors for surface flaws in a tubular member

In the safety assessment of pressure vessels and pipes with circumferential surface cracks, it is often necessary to consider fatigue crack propagation and fracture among the possible modes of failure. The stress intensity factors at crack tips are important parameters for estimating residual life and criticality. The purpose of this paper is to present a method to calculate the mode I stress intensities for semi-elliptical cracks in pipes. This method uses the finite element technique to analyse a crack but does not require the crack to be modelled explicitly. This method is ideal for use with either fatigue life calculations or use with structural optimisation processes. Accurate results are obtained using only a relatively small number of degrees of freedom without the need to explicitly mesh cracks. In this paper a range of examples are presented to demonstrate the accuracy of this method.     

Stochastic aspects of bridge deck aeroelasticity under turbulent flow

Returning to an earlier frequency-domain analysis of the problem of long-span bridge response to ambient winds, the paper emphasizes the indispensable experimental information necessary to bring results into conformity with full-scale prototype action. Focus is placed upon the use of a sectional wind tunnel model under simulated turbulent flow as the prime source of this information, which consists principally of the flutter derivatives and the spectra of the wind forces, both obtained under turbulent flow. The effect of three-dimensional turbulence upon the flutter derivatives is observed to influence structural stability in a manner consistent with that observed in full-bridge wind tunnel models.     

Singularities of Fourier transforms: A tribute to M. J. Lighthill

Some singular generalised functions of several variables are introduced and their properties described. They are used to support some general theorems to the effect that (a) the singularities of a generalised function are responsible for the behaviour of its Fourier transform at infinity and (b) the behaviour of a generalised function at infinity determines the singularities of its Fourier transform.     

Scrapie infection of transgenic mice leads to network and intrinsic dysfunction of cortical and hippocampal neurones

The human prion encephalopathy Creutzfeldt-Jakob disease often is manifest as rapidly progressing dementia with myoclonus and synchronous, periodic discharges. To investigate the electrophysiology of prion disease we used intra- and extra-cellular recordings from brain slices from Tg(SHaPrP+/+) 81 mice, which express Syrian hamster prion protein and which are susceptible to hamster-passaged scrapie isolates. Forty days after intracerebral inoculation with scrapie isolate Sc237, we recorded prolonged, epileptiform discharges in cortex and hippocampus. Neurological signs were subtle and histopathology was minimal. Central nervous system (CNS) dysfunction progressed; by 57 days the mice were ataxic, had spongiform histopathology and they died in <63 days. During the terminal phase, intrinsic neuronal properties changed dramatically and action potentials broadened from <4 to 20-100 ms in 30% of cortical cells. We conclude that brain dysfunction in experimental scrapie precedes clinical signs and spongiform histopathology, and is preserved in slices maintained in vitro, making it accessible to electrophysiological analysis.     

Characterization of a calmodulin-binding transporter from the plasma membrane of barley aleurone

We have used Arabidopsis calmodulin (CaM) covalently coupled to horseradish peroxidase to screen a barley aleurone cDNA expression library for CaM binding proteins. The deduced amino acid sequence of one cDNA obtained by this screen was shown to be a unique protein of 702 amino acids with CaM and cyclic nucleotide binding domains at the carboxyl terminus and high similarity to olfactory and K+ channels. This cDNA was designated HvCBT1 (Hordeum vulgare CaM binding transporter). Hydropathy plots of HvCBT1 showed the presence of six putative transmembrane domains, but sequence alignment indicated a pore domain that was unlike the consensus domains in K+ and olfactory channels. Expression of a subclone of amino acids 482-702 in Escherichia coli generated a peptide that bound CaM. When a fusion protein of HvCBT1 and green fluorescent protein was expressed in barley aleurone protoplasts, fluorescence accumulated in the plasma membrane. Expression of HvCBT1 in the K+ transport deficient Saccharomyces cerevisiae mutant CY162 showed no rescue of the mutant phenotype. However, growth of CY162 expressing HvCBT1 with its pore mutated to GYGD, the consensus sequence of K+ channels, was compromised. We interpret these data as indicating that HvCBT1 acts to interfere with ion transport.     

Intravenous RMP-7 increases delivery of ganciclovir into rat brain tumors and enhances the effects of herpes simplex virus thymidine kinase gene therapy

Herpes simplex virus thymidine kinase (HSV-tk) gene therapy for brain tumors depends on ganciclovir (GCV) and its transport across the blood-brain tumor barrier (BBTB). We examined whether RMP-7, the bradykinin analog and potent BBTB permeabilizer, could enhance the efficacy of GCV treatment of brain tumors by increasing the BBTB delivery of GCV. In vitro, a significant bystander cytocidal effect of GCV was shown in mixed HSV-tk-transduced (HSV-tk+) and control vector-transduced (HSV-tk-) C6 glioma cultures. A dose-dependent cytotoxic effect of GCV on untransformed C6 cells was also shown. In vivo, rats with 100% HSV-tk+ or 100% HSV-tk- intracerebral C6 gliomas were treated for 7 days with intravenous infusions of GCV alone or with GCV and RMP-7 (2.5 microg/kg/day). The growth of HSV-tk+ and HSV-tk- gliomas decreased with increasing doses of GCV. A high dosage (100 mg of GCV/kg/day) eradicated all HSV-tk- and HSV-tk+ tumors. An intermediate dosage (5 mg of GCV/kg/day) reduced the growth of HSV-tk- gliomas by 42% if given alone, and by 88% in combination with RMP-7. A low dosage (0.5 mg of GCV/kg/day) in combination with RMP-7 enhanced the regression of HSV-tk+ gliomas by 87% compared with GCV alone. Low-dose GCV was ineffective in HSV-tk- tumors. RMP-7 increased [3H] GCV tumoral uptake by 2.6- and 1.7-fold in the tumor center and periphery, respectively. We conclude that RMP-7 could be an important adjunctive treatment for suicide gene therapy of brain tumors, while an RMP-7/GCV combination may also have a significant antitumor effect in untransfected gliomas.     

The Columnar-to-Equiaxed Transition in Melt Pools During Laser Powder Bed Fusion of M2 Steel

Metallurgical and Materials Transactions A - This work integrates experimental and numerical methods to determine the process conditions under which the columnar-to-equiaxed transition (CET)...     

爆炸荷载下钢筋混凝土简支板的有限差分分析

考虑应变率效应、剪切和弯曲变形、横断面几何尺寸、荷载情况,编制有限差分分析程序,精确有效地分析爆炸荷载下钢筋混凝土简支板的动力响应。与构件截面应变速率相适应,采用截面分层分析模型,建立截面矩与和曲率的关系。根据所提公式,将相应的应变率效应与截面分层分析模型相结合,沿构件长度方向,对构件纵向应变速率的分布进行评估。采用明确的有限差分方法,可得到包括剪切变形和转动变量的Timoshenko梁方程的数值解。结合爆炸量和距离,根据钢筋混凝土板爆炸试验的结果,验证所提有限差分分析模型的精确性。与传统的单自由度分析和有限元分析相比,有限差分分析程序快速、精确,结合了单自由度分析的速度和有限元分析精确的优势,十分适合于设计公司应用。