Heavy Meson Physics: What have we learned in Twenty Years?

I give a personal account of the development of the field of heavy quarks. After reviewing the experimental discovery of charm and bottom quarks, I describe how the field's focus shifted towards determination of CKM elements and how this has matured into a precision science.Comment: This talk was presented during the ceremony awarding the Medalla 2003 of the Division of Particles and Fields of The Mexican Phsyical Society, at the IX Mexican Workshop on Particles and Fields; submitted for proceedings; 9 pages, 9 figures; replacement: fix multiple typo

Density of Surface States in Discrete Models

We consider a simple quantum model with a surface and prove the existence of a surface density of states. We show that the energy spectrum of the model is the union of the support of the bulk densities of states of the media forming the surface and the support of the surface density of states

Evaluation of SMAP Freeze/Thaw Retrieval Accuracy at Core Validation Sites in the Contiguous United States

Seasonal freeze-thaw (FT) impacts much of the northern hemisphere and is an important control on its water, energy, and carbon cycle. Although FT in natural environments extends south of 45°N, FT studies using the L-band have so far been restricted to boreal or greater latitudes. This study addresses this gap by applying a seasonal threshold algorithm to Soil Moisture Active Passive (SMAP) data (L3_SM_P) to obtain a FT product south of 45°N (‘SMAP FT’), which is then evaluated at SMAP core validation sites (CVS) located in the contiguous United States (CONUS). SMAP landscape FT retrievals are usually in good agreement with 0–5 cm soil temperature at SMAP grids containing CVS stations (\u3e70%). The accuracy could be further improved by taking into account specific overpass time (PM), the grid-specific seasonal scaling factor, the data aggregation method, and the sampling error. Annual SMAP FT extent maps compared to modeled soil temperatures derived from the Goddard Earth Observing System Model Version 5 (GEOS-5) show that seasonal FT in CONUS extends to latitudes of about 35–40°N, and that FT varies substantially in space and by year. In general, spatial and temporal trends between SMAP and modeled FT were similar

Time series of high resolution spectra of SN 2014J observed with the TIGRE telescope

We present a time series of high resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS echelle spectrograph installed at the 1.2 m TIGRE telescope. We present a series of 33 spectra with a resolution of R = 20, 000, which covers the important bright phases in the evolution of SN 2014J during the period from January 24 to April 1 of 2014. The spectral evolution of SN 2014J is derived empirically. The expansion velocities of the Si II P-Cygni features were measured and show the expected decreasing behaviour, beginning with a high velocity of 14,000 km/s on January 24. The Ca II infrared triplet feature shows a high velocity component with expansion velocities of > 20, 000 km/s during the early evolution apart from the normal component showing similar velocities as Si II. Further broad P-Cygni profiles are exhibited by the principal lines of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very sharp Na I D doublet absorption components. Our analysis suggests interesting substructures in the interstellar medium of the host galaxy M82, as well as in our Milky Way, confirming other work on this SN. We were able to identify the interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 A as well as K I at 7664 and 7698 A. Furthermore, we confirm several Diffuse Interstellar Bands, at wavelengths of 6196, 6283, 6376, 6379 and 6613 A and give their measured equivalent widths.Comment: 11 pages, 10 figures, accepted for publication in MNRA

Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy

Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples

Globular Clusters in the dE,N galaxy NGC 3115 DW1: New Insights from Spectroscopy and HST Photometry

The properties of globular clusters in dwarf galaxies are key to understanding the formation of globular cluster systems, and in particular in verifying scenarios in which globular cluster systems of larger galaxies formed (at least partly) from the accretion of dwarf galaxies. Here, we revisit the globular cluster system of the dE,N galaxy NGC 3115 DW1 - a companion of the nearby S0 galaxy NGC 3115 - adding Keck/LRIS spectroscopy and HST/WFPC2 imaging to previous ground-based photometry. Spectra for seven globular clusters reveal normal abundance ratios with respect to the Milky Way and M31 clusters, as well as a relatively high mean metallicity ([Fe/H] = -1.0+/-0.1 dex). Crude kinematics indicate a high velocity dispersion within 10 kpc which could either be caused by dark matter dominated outer regions, or by the stripping of outer globular clusters by the nearby giant galaxy NGC 3115. The total galaxy mass out to 3 and 10 kpc lies between 10^10 and 10^11 solar masses and 2*10^10 and 4*10^11 solar masses, respectively, depending on the mass estimator used and the assumptions on cluster orbits and systemic velocity. The HST imaging allows measurement of sizes for two clusters, returning core radii around 2.0 pc, similar to the sizes observed in other galaxies. Spectroscopy allows an estimate of the degree of contamination by foreground stars or background galaxies for the previous ground-based photometry, but does not require a revision of previous results: NGC 3115 DW1 hosts around 60+/-20 clusters which corresponds to a specific frequency of 4.9+/-1.9, on the high end for massive dEs. Given its absolute magnitude (M_V=-17.7 mag) and the properties of its cluster system, NGC 3115 DW1 appears to be a transition between a luminous dE and low-luminosity E galaxy.Comment: 25 pages, 8 figures, accepted for publication in The Astronomical Journal, August 2000 issu

Ohmic contacts to n-type germanium with low specific contact resistivity

A low temperature nickel process has been developed that produces Ohmic contacts to n-type germanium with specific contact resistivities down to (2.3 ± 1.8) x10<sup>-7</sup> Ω-cm<sup>2</sup> for anneal temperatures of 340 degC. The low contact resistivity is attributed to the low resistivity NiGe phase which was identified using electron diffraction in a transmission electron microscope. Electrical results indicate that the linear Ohmic behaviour of the contact is attributed to quantum mechanical tunnelling through the Schottky barrier formed between the NiGe alloy and the heavily doped n-Ge.<p></p&gt

Speciation of cadmium mixed ligand complexes in salt water lakes

Amalgam voltammetry has been used to study heavy metal interaction in model lake water in KNO3 at 23 oC at concentration levels of genuine lake water. The hanging drop amalgam electrode was prepared in situ before exchanging the medium for the sample solution. Half-wave potentials at two metal ion concentrations were measured, one at the actual concentration in the lake while the other at a much lower one. The experimentally determined shifts in half-wave potentials are used to compute several formation constants. At the natural [CO32-] of 0.5 M in the lake, the main contributor to the speciation of cadmium is [Cd(CO3Cl2)]2-. At high [Cd2+], the DPASV detects the presence of free Cd2+ ions, hence, potential polluting effect, while the amalgam reports [Cd(CO3)2Cl)]3- to be dominant above [CO32-] = 0.8 M. There is a variation in the number of complexes detected, their stabilities and percentage distribution in the two methods. Cd2+ ion concentration also affects the number of complexes formed and their stabilities. KEY WORDS: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes  Bull. Chem. Soc. Ethiop. 2003, 17(1), 85-94

Generalized four-point characterization method for resistive and capacitive contacts

In this paper, a four-point characterization method is developed for resistive samples connected to either resistive or capacitive contacts. Provided the circuit equivalent of the complete measurement system is known including coaxial cable and connector capacitances as well as source output and amplifier input impedances, a frequency range and capacitive scaling factor can be determined, whereby four-point characterization can be performed. The technique is demonstrated with a discrete element test sample over a wide frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The data fit well with a circuit simulation of the entire measurement system. A high impedance preamplifier input stage gives best results, since lock-in input impedances may differ from manufacturer specifications. The analysis presented here establishes the utility of capacitive contacts for four-point characterizations at low frequency.Comment: 21 pages, 10 figure