Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium

We report x-ray reflectivity (XR) and small angle off-specular diffuse scattering (DS) measurements from the surface of liquid Indium close to its melting point of $156^\circ$C. From the XR measurements we extract the surface structure factor convolved with fluctuations in the height of the liquid surface. We present a model to describe DS that takes into account the surface structure factor, thermally excited capillary waves and the experimental resolution. The experimentally determined DS follows this model with no adjustable parameters, allowing the surface structure factor to be deconvolved from the thermally excited height fluctuations. The resulting local electron density profile displays exponentially decaying surface induced layering similar to that previously reported for Ga and Hg. We compare the details of the local electron density profiles of liquid In, which is a nearly free electron metal, and liquid Ga, which is considerably more covalent and shows directional bonding in the melt. The oscillatory density profiles have comparable amplitudes in both metals, but surface layering decays over a length scale of $3.5\pm 0.6$ \AA for In and $5.5\pm 0.4$ \AA for Ga. Upon controlled exposure to oxygen, no oxide monolayer is formed on the liquid In surface, unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.

Holistic Analysis of the Classroom

Should we judge the quality of the class by the grades the students and teacher get at the end of the semester or how the group collaborated during the semester towards acquiring new knowledge? Up until recently, the later approach was all too inaccessible due to complexity and time needed to evaluate every class. With the development of new technologies in different branches of video processing, gaze tracking and audio analysis we are getting the opportunity to go further with our analysis and go around the potential problem substitution into which we were previously forced. We present our efforts to record student-student and student-teacher interactions within a classroom eco-system. For this purpose, we developed a multi-camera system for observing teacher actions and students reactions throughout the class. We complemented the data with a mobile eye-tracker worn by the teacher, quantitative questionnaire data collection, as well as in-depth interviews with students about their impressions of the classes they took, and about our intervention. The seven-part experiment was conducted during the autumn semester of 2013, in two classes with over 60 participants. We present the conclusions we reached about the experiment format, visualize the preliminary results of our processing and discuss other options we are considering for our further experiments. We aim to explore further possibilities for analysing classroom life in order to create a more responsive environment to the needs of the students

Detection of 15NH2D in dense cores: A new tool for measuring the 14N/15N ratio in the cold ISM

Ammonia is one of the best tracers of cold dense cores. It is also a minor constituent of interstellar ices and, as such, one of the important nitrogen reservoirs in the protosolar nebula, together with the gas phase nitrogen, in the form of N2 and N. An important diagnostic of the various nitrogen sources and reservoirs of nitrogen in the Solar System is the 14N/15N isotopic ratio. While good data exist for the Solar System, corresponding measurements in the interstellar medium are scarce and of low quality. Following the successful detection of the singly, doubly, and triply deuterated isotopologues of ammonia, we have searched for 15NH2D in dense cores, as a new tool for investigating the 14N/15N ratio in dense molecular gas. With the IRAM-30m telescope, we have obtained deep integrations of the ortho 15NH2D (1(1,1)-1(0,1)) line at 86.4 GHz, simultaneously with the corresponding ortho NH2D line at 85.9 GHz. o-15NH2D is detected in Barnard-1b, NGC1333-DCO+, and L1689N, while we obtained upper limits towards LDN1544 and NGC1333-IRAS4A, and a tentative detection towards L134N(S). The 14N/15N abundance ratio in NH2D ranges between 350 and 850, similar to the protosolar value of ~ 424, and likely higher than the terrestrial ratio of 270

Tunable bistable hysteresis of the magnetic resonance of conduction electrons in solids

Under dynamic nuclear polarisation by the Overhauser effect, conduction electrons in solids can exhibit a hysteresis of their magnetic resonance. In the case of polycrystalline samples of β-Ga2O3, a giant hysteresis can be achieved corresponding to a situation where the electron spins absorb the electromagnetic field when the magnetic field is swept downward and no absorption occurs in the reverse sweep direction. It is shown that this phenomenon is a general property of conducting solids containing elements with non-zero nuclear spins

ELECTROCHEMISTRY OF 9,9'-BIFLUORENYLIDENE - DETECTION OF THE RADICAL SPECIES BY SPECTROELECTROCHEMICAL AND EPR METHODS

It is shown by cyclic voltammetry and differential pulse polarography that 9,9'-bifluorenylidene (BFD) undergoes two successive reduction waves in aprotic solvents corresponding to two monoelectronic transfers: a reversible (E1 = - 1.10 V SCE) followed by a quasi-reversible (E2 = - 1.50 V SCE) couple. These were monitored by spectrochemical methods and kinetic data were obtained for the individual monoelectronic transfers. The monoradical was detected by EPR, and the spectrum interpreted in terms of delocalization of the unpaired electron on the two fluorenyl fragments