Heating and Cooling Dynamics of Carbon Nanotubes Observed by Temperature-Jump Spectroscopy and Electron Microscopy

Microscopy imaging indicates that in situ carbon nanotubes (CNTs) irradiation with relatively low dosages of infrared radiation results in significant heating of the tubes to temperatures above 1300 K. Ultrafast temperature-jump experiments reveal that CNTs laser-induced heating and subsequent cooling in solution take tens and hundreds of picoseconds, respectively. Given the reported transient behavior, these observations suggest novel ways for a T-jump methodology, unhindered by the requirement for excitation of water in the study of biological structures. They also provide the rate information needed for optimization of photothermal therapy that invokes infrared irradiation to selectively heat and annihilate cancer cells

Scanning ultrafast electron microscopy

Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability

A New Monte Carlo Based Algorithm for the Gaussian Process Classification Problem

Gaussian process is a very promising novel technology that has been applied to both the regression problem and the classification problem. While for the regression problem it yields simple exact solutions, this is not the case for the classification problem, because we encounter intractable integrals. In this paper we develop a new derivation that transforms the problem into that of evaluating the ratio of multivariate Gaussian orthant integrals. Moreover, we develop a new Monte Carlo procedure that evaluates these integrals. It is based on some aspects of bootstrap sampling and acceptancerejection. The proposed approach has beneficial properties compared to the existing Markov Chain Monte Carlo approach, such as simplicity, reliability, and speed

4D Scanning Ultrafast Electron Microscopy: Visualization of Materials Surface Dynamics

The continuous electron beam of conventional scanning electron microscopes (SEM) limits the temporal resolution required for the study of ultrafast dynamics of materials surfaces. Here, we report the development of scanning ultrafast electron microscopy (S-UEM) as a time-resolved method with resolutions in both space and time. The approach is demonstrated in the investigation of the dynamics of semiconducting and metallic materials visualized using secondary-electron images and backscattering electron diffraction patterns. For probing, the electron packet was photogenerated from the sharp field-emitter tip of the microscope with a very low number of electrons in order to suppress space–charge repulsion between electrons and reach the ultrashort temporal resolution, an improvement of orders of magnitude when compared to the traditional beam-blanking method. Moreover, the spatial resolution of SEM is maintained, thus enabling spatiotemporal visualization of surface dynamics following the initiation of change by femtosecond heating or excitation. We discuss capabilities and potential applications of S-UEM in materials and biological science

Picosecond photofragment spectroscopy. II. The overtone initiated unimolecular reaction H_2O_2(v_(OH)=5)→2OH

This paper, second in the series, reports on the picosecond time‐resolved photofragmentation of the overtone (v_(OH)=5) initiated reaction: HOOH+hν→2OH. The hydrogen peroxide is initially excited by way of a picosecond laser pulse to the fourth overtone level of the OH‐stretch local mode. The subsequent unimolecular reaction behavior is obtained by monitoring the laser‐induced fluorescence, caused by the picosecond probe–pulse electronic excitation of the OH radical photoproduct (in a given rotational state). The two pulses are scanned relative to one another in time thereby mapping out the product yield for the given delay‐time interval. The resultant product formation behavior is found to be nonexponential, and may be modeled as a biexponential rise. Furthermore, the quasibiexponential behavior is sensitive to the exact excitation wavelength—slight variations of which result in large changes in the two time constants and the relative amplitudes of the fast and slow components. These experiments give direct evidence for the inhomogeneous nature of the overtone transition on the picosecond time scale, and provide the dissociation rate contribution to the homogeneous width (0.05–0.15 cm^(−1)). The apparent width for the main band feature is about 200 cm^(−1). The rate of product formation (magnitude and form) is interpreted in terms of statistical and nonstatistical theories. The limitations of the applicability of each model is discussed. The fluctuations of the fitting parameters as a function of excitation wavelength may be simulated by a statistical model which considers all possible discrete optical transitions within the simulated laser bandwidth and the details of product formation from each state. For a nonstatistical interpretation, the biexponential form reflects a division of the vibrational phase space, and this is discussed in the spirit of a kinetic model. Finally, experimental results are reported for direct UV initiated photofragmentation. The observed dynamics indicate that a very different type of potential surface (repulsive) is involved, in contrast to the overtone initiated dissociation, which takes place on the ground state surface

Childhood development stages and learning on global issues

This helpdesk report provides a summary of available literature and evidence relating to childhood development stages; specifically, when is the best time to influence children’s thinking on global issues. This question is related to a second query covered in a separate helpdesk report that examines the development education landscape in the UK: specifically, what else apart from British Council’s Connecting Classrooms Programme is going on to build partnerships between schools in the UK and schools overseas? How many children/schools are part of something like this? These helpdesk reports are designed to help inform a business case and guide the Department for International Development’s thinking for a new approach to delivering development education in the UK when the current phases of Connecting Classrooms and the Global Learning Programme ends. K4D helpdesk reports provide summaries of current research, evidence and lessons learned. This report was commissioned by DFID

CLEMASTINE, THE H1 HISTAMINE RECEPTOR ANTAGONIST, ALTERS THE HUMAN SEX AND THYROID HORMONAL PROFILES

  Objective: Clemastine is widely used as an antihistaminic drug. However, clemastine effectively acts as an antagonist of H1 histamine receptor, it has significant burden adverse effects causing common nervous system, psychiatric, and gastrointestinal ailments, as well as rare cardiac and immune system disorders. The objective of this study is to investigate whether there is a remarkable impact of clemastine administration on the human hormonal pituitary-thyroid-adrenal axis.Methods: To achieve that, hormonal profile was tested in the sera of males and females treated and untreated individuals with clemastine. This is to measure serum estradiol, follicle-stimulating hormone, luteinizing hormone, prolactin, progesterone, dehydroepiandrosterone sulfate, thyroid-stimulating hormone, triiodothyronine, thyroxine, fasting insulin, and cortisol levels. The circulating hormonal levels were measured quantitatively using enzyme-link immunosorbent assay.Results: We resulted that there were significant differences of the human hormonal profile on clemastine treatment.Conclusion: Hormonal profiling showed that there were remarkable signatures could be of great interest to underline some recommendations and guidelines optimizing the clemastine dosage to avoid burdens associated with the administration of this drug as well as maintain the physiological and psychological performances of both sexes exposing to clemastine during the period of allergic treatment