Computational Study of the Structure and Thermodynamic Properties of Ammonium Chloride Clusters Using a Parallel J-Walking Approach

The thermodynamic and structural properties of (NH$_4$Cl)$_n$ clusters, n=3-10 are studied. Using the method of simulated annealing, the geometries of several isomers for each cluster size are examined. Jump-walking Monte Carlo simulations are then used to compute the constant-volume heat capacity for each cluster size over a wide temperature range. To carry out these simulations a new parallel algorithm is developed using the Parallel Virtual Machine (PVM) software package. Features of the cluster potential energy surfaces, such as energy differences among isomers and rotational barriers of the ammonium ions, are found to play important roles in determining the shape of the heat capacity curves.Comment: Journal of Chemical Physics, accepted for publicatio

Bessel Functions in Mass Action. Modeling of Memories and Remembrances

Data from experimental observations of a class of neurological processes (Freeman K-sets) present functional distribution reproducing Bessel function behavior. We model such processes with couples of damped/amplified oscillators which provide time dependent representation of Bessel equation. The root loci of poles and zeros conform to solutions of K-sets. Some light is shed on the problem of filling the gap between the cellular level dynamics and the brain functional activity. Breakdown of time-reversal symmetry is related with the cortex thermodynamic features. This provides a possible mechanism to deduce lifetime of recorded memory.Comment: 16 pages, 9 figures, Physics Letters A, 2015 in pres

The visual perception of motion

Sensing the movements of the world and the objects within it appears to be a fundamental job for our visual system. In rare cases of brain damage, we find that individuals lacking motion perception live in a very different world of frozen images, where simple tasks like filling a kettle or crossing the road take on alarming difficulties. That tasks such as driving a fast car down the freeway require a good sense of the movements of yourself and other objects are obvious, but motion information is used in many less obvious ways. For example, it may seem a trivial task to us to follow a moving object with our eyes, but without motion perception these smooth pursuit eye movements are not possible. One way to show this is to have people attempt to move their eyes smoothly along a line etched on a wall. At the same time we place a very bright light just under this line. The bright light burns an afterimage into the retina which can then be examined at leisure. In attempting the eye movement we find that the afterimage is not a smooth line but a series of ‘dots’. This is because you find it difficult to smoothly move yours eyes along the line – even more so if it is vertical – instead flicking your eyes in a series of small, fast jumps known as saccades. Each dot represents the alighting point of a saccade and each gap the distance moved by the saccade. Now, if the line is replaced with a moving dot and we try to track this, the resulting afterimage is a smooth line. This shows that our eyes moved at a constant rate so that the very centre of our vision, where it is best at seeing fine detail, remained focused on the target. Not surprisingly, damage to areas of the brain involved in analysing the moving image destroys this ability

An exploratory study of teachers\u27 views of knowledge acquisition

This exploratory investigation examined relations between teachers\u27 views of knowledge acquisition and their use of computers in the classroom. A survey instrument that assessed views ranging from objectivism to constructivism is described; and teaching experience, demographic variables, and types of software programs likely to be used are discussed

On the Interaction and Coalescence if Spherical Blast Waves

The scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed. Both point source explosions and high pressure gas explosions are considered. Test data on blast overpressure from the interaction and coalescence of spherical blast waves emanating from explosives in the form of shaped charges of different strength placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure. The results point out the possibility of detecting source explosions from far-field pressure measurements

Rates of erosion and landscape change along the Blue Ridge escarpment, southern Appalachian Mountains, estimated from in situ cosmogenic 10Be

The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the lower-elevation Piedmont and higher-elevation Blue Ridge physiographic provinces. To understand better the rate at which this landform and the adjacent landscape are changing, we measured cosmogenic 10Be in quartz separated from sediment samples (n = 50) collected in thirty-two streams and from three exposed bedrock outcrops along four transects normal to the escarpment, allowing us to calculate erosion rates integrated over 104–105 years. These basin-averaged erosion rates (5.4–49 m My-1) are consistent with those measured elsewhere in the southern Appalachians and show a positive relationship between erosion rate and average basin slope. Erosion rates show no relationship with basin size or relative position of the Brevard fault zone, a fundamental structural element of the region. The cosmogenic isotopic data, when considered along with the distribution of average basin slopes in each physiographic province, suggest that the escarpment is eroding on average more rapidly than the Blue Ridge uplands, which are eroding more rapidly than the Piedmont lowlands. This difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates

Ab initio many-body calculations of nucleon scattering on 4He, 7Li, 7Be, 12C and 16O

We combine a recently developed ab initio many-body approach capable of describing simultaneously both bound and scattering states, the ab initio NCSM/RGM, with an importance truncation scheme for the cluster eigenstate basis and demostrate its applicability to nuclei with mass numbers as high as 17. Using soft similarity renormalization group evolved chiral nucleon-nucleon interactions, we first calculate nucleon-4He phase shifts, cross sections and analyzing power. Next, we investigate nucleon scattering on 7Li, 7Be, 12C and 16O in coupled-channel NCSM/RGM calculations that include low-lying excited states of these nuclei. We check the convergence of phase shifts with the basis size and study A=8, 13, and 17 bound and unbound states. Our calculations predict low-lying resonances in 8Li and 8B that have not been experimentally clearly identified yet. We are able to reproduce reasonably well the structure of the A=13 low lying states. However, we find that A=17 states cannot be described without an improved treatment of 16O one-particle-one-hole excitations and alpha clustering.Comment: 18 pages, 20 figure