Critical Evaluation and Compilation of Viscosity and Diffusivity Data Semiannual Status Report No. 1, Jul. 1 - Dec. 31, 1965

Compilation and evaluation of diffusivity and viscosity data on gas and liquid turbulent flow system

Evidence for crossed Andreev reflection in superconductor-ferromagnet hybrid structures

We have measured the non-local resistance of aluminum-iron spin-valve structures fabricated by e-beam lithography and shadow evaporation. The sample geometry consists of an aluminum bar with two or more ferromagnetic wires forming point contacts to the aluminum at varying distances from each other. In the normal state of aluminum, we observe a spin-valve signal which allows us to control the relative orientation of the magnetizations of the ferromagnetic contacts. In the superconducting state, at low temperatures and excitation voltages well below the gap, we observe a spin-dependent non-local resistance which decays on a smaller length scale than the normal-state spin-valve signal. The sign, magnitude and decay length of this signal is consistent with predictions made for crossed Andreev reflection (CAR).Comment: RevTeX, 4 page

CO2 Increase: Questions Beyond Climate Change

The increase of the tropospheric C02 (carbon dioxide) concentration is considered by scientists all over the world to be an alarming signal, as becomes evident from the huge amount of literature on the subject. The so-called greenhouse-gas effect, or, more precisely, its anthropogenic component, is mainly caused by the C02 increase. However, other trace gases have also contributed their share. Far-reaching climatic changes, a temperature increase in the tropospheric air, especially in the polar region, as well as a gradual melting of the Greenland and Antarctic ice with a simultaneous rise of the seawater level, are being predicted as a consequence of the greenhouse effect. In addition to these gloomy prospects a new hypothesis has developed: The biological consequences of the evolution of a changed composition of the air could be hazardous to man and nature

Dimensionality effects on non-equilibrium electronic transport in Cu nanobridges

We report on non-equilibrium electronic transport through normal-metal (Cu) nanobridges coupled to large reservoirs at low temperatures. We observe a logarithmic temperature dependence of the zero-bias conductance, as well as a universal scaling behavior of the differential conductance. Our results are explained by electron-electron interactions in diffusive metals in the zero-dimensional limit.Comment: RevTex, 4 page

Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators

Whispering gallery resonators (WGR's), based on total internal reflection, possess high quality factors in a broad spectral range. Thus, nonlinear optical processes in such cavities are ideally suited for the generation of broadband or tunable electromagnetic radiation. Experimentally and theoretically, we investigate the tunability of optical parametric oscillation in a radially structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal and idler waves are tuned from 1.78 to 2.5 \mum - including the point of degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak off-centering of the radial domain structure extends considerably the tuning capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure

DEM Simulation of Concrete Fracture Phenomena

Concrete fracture phenomena are investigated in this work. It is the fracture processes and failure mechanisms which are specifically investigated rather than the reaching of a certain maximum load or the investigation of the concrete’s behaviour within a range of safe working loads. The following questions are addressed. How do the crack positions vary from one test to another? Is it possible to identify in advance where for example micro-cracks will emerge to a global macro-crack later on? In order to investigate this matter, a two-dimensional numerical simulation based on the Discrete Element Method (DEM) is used for the analysis of concrete behaviour under compression load. Frictional behaviour, crack initiation and damage evolution are analysed. Regarding the concrete body, convex and concave geometries can be treated. The cracks are discrete just as in real laboratory experiments. The cracks arise due to the interaction of the concrete particle elements and without the predefinition of any crack zones or crack elements. The simulation results are compared to the ones of laboratory experiments. The ratio of longitudinal strain to lateral strain is obtained as a result of the simulation and compared to experimental results. The qualitative evolution of postprocessing entities such as stresses and strains is analysed

Contacting single bundles of carbon nanotubes with alternating electric fields

Single bundles of carbon nanotubes have been selectively deposited from suspensions onto sub-micron electrodes with alternating electric fields. We explore the resulting contacts using several solvents and delineate the differences between Au and Ag as electrode materials. Alignment of the bundles between electrodes occurs at frequencies above 1 kHz. Control over the number of trapped bundles is achieved by choosing an electrode material which interacts strongly with the chemical functional groups of the carbon nanotubes, with superior contacts being formed with Ag electrodes.Comment: 4 pages, RevTe

Nuclear spin relaxation by intramolecular interactions in gases of homonuclear diatomic molecules

The differential equations which describe the relaxation of macroscopic observables associated with nuclear spins in homonuclear diatomic molecules are derived using an expansion of the nuclear spin density matrix in terms of irreducible tensors. It is shown, using an intramolecular quadrupole mechanism, that the only difference between nuclear spin relaxation of the ortho- and para-species arises from the rotational states being restricted to odd and even values. This difference is vanishingly small at high temperatures so that the relaxation equations for nuclear magnetization become identical for both species. A previous paper predicting a difference even at high temperatures is shown to be in error and is corrected

Toy for Preschoolers with Deaf-Blindness

There are approximately 70,000-100,000 people living in America that are diagnosed as deaf-blind. Since children with deaf-blindness are an extreme minority in the US, research, toys and technological advancements for these children get overlooked. As a result, the developmental processes of children with deaf-blindness are delayed by several years, compared to normal children, due to the lack of resources available to encourage learning. According to Virginia’s Department of Education standards of learning for preschoolers, development physically, mathematically,of environmental awareness and of a sense of self are core requirements for Kindergarten. Therefore, there is a need for a toy that will provide stimulation to develop physical, social, and cognitive progression to keep children with deaf-blindness on a normal learning curve. Our design consists of components each of which stimulate one of the development goals. The first component is a chair that promotes proper posture. The second component is a colored and vibrating drum game to stimulate mathematical development through pattern recognition. The third component is a Braille exposure game to stimulate literacy development, by associating a Braille word with an object or concept. The fourth component is an apparatus that can be placed over the chair that contains dangling objects where the child can reach out to explore their surrounding environment. Under the supervision and interaction of a parent/guardian, the child will develop socially through human interaction and feedback suggested in the provided instruction manual. Our team has been conducting research online and consulting professionals that have worked, or are currently working, in the deaf-blind field; therefore we gathered information on how children with deaf-blindness typically react to certain stimuli and various developmental concerns, to aid with the design of the toy components. With this foundation, our group drafted a variety of design concepts. We weighed out the positives, negatives, and overall efficiency of each concept which lead us to produce our final design. Then we presented our final design to our faculty advisor, perfect our idea and move forward with materials selection. Our next step in the design process is to test the efficiency of different materials and methods that we selected for the stimulatory components through experimentation and computation of engineering principles behind the design. Unfortunately our group encountered a problem in the design process, we are behind in the construction of the chair components due to the amount of time it took to complete the machine shop class. Once our testing is completed, we will begin to construct and complete the full prototype of our product.https://scholarscompass.vcu.edu/capstone/1003/thumbnail.jp