Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions

The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions

Thermal expansion of the spin-1/2 Heisenberg-chain compound Cu(C4_4H4_4N2_2)(NO3_3)2_2

Compounds containing magnetic subsystems representing simple model spin systems with weak magnetic coupling constants are ideal candidates to test theoretical predictions for the generic behavior close to quantum phase transitions. We present measurements of the thermal expansion and magnetostriction of the spin-1/2-chain compound copper pyrazine dinitrate Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$. Of particular interest is the low-temperature thermal expansion close to the saturation field $H_c \simeq 13.9 \mathrm{T}$, which defines a quantum phase transition from the gapless Luttinger liquid state to the fully saturated state with a finite excitation gap. We observe a sign change of the thermal expansion for the different ground states, and at the quantum critical point $H_c$ the low-temperature expansion approaches a $1/\sqrt{T}$ divergence. Thus, our data agree very well with the expected quantum critical behaviour.Comment: 4 pages, 3 figures; to appear in the proceedings of the ICM 09 held in Karlsruhe, German

Dynamic Visualizations for the Analysis of Desert Tortoise Telemetry and Habitat in Joshua Tree National Park

Joshua Tree National Park (JOTR) has been monitoring their desert tortoise population’s telemetry since 2005 using transmitters attached to as many as 18 tortoises. JOTR needed to visualize tortoise telemetry data and temporal environmental datasets to see what factors may be affecting the movements of the tortoises. JOTR also needed to look at the telemetry data in relation to roads to see if curbing implementations have been effective. The foundation for this project is ArcMap™. This project includes various tools written in Python within ArcMap’s toolboxes that allow for automated data manipulation and analysis of the various datasets. These tools prepare the datasets for dynamic visualizations of the data in Google Earth®. Additionally, the preparation of the data will also enable it to be exploited by ArcGIS 10’s integrated time-visualization capability. ArcGIS Explorer™ can also be used to perform similar dynamic visualizations as Google Earth. The provided tools and visualizations aim to provide JOTR with a means to help analyze and monitor their tortoise population to improve their survivability

Signature of nearly icosahedral structures in liquid and supercooled liquid Copper

A growing body of experiments display indirect evidence of icosahedral structures in supercooled liquid metals. Computer simulations provide more direct evidence but generally rely on approximate interatomic potentials of unproven accuracy. We use first-principles molecular dynamics simulations to generate realistic atomic configurations, providing structural detail not directly available from experiment, based on interatomic forces that are more reliable than conventional simulations. We analyze liquid copper, for which recent experimental results are available for comparison, to quantify the degree of local icosahedral and polytetrahedral order