Revitalization and Initial Testing of a Blowdown Supersonic Wind Tunnel

The Supersonic tunnel located in Patterson Labs at Mississippi State University has been thoroughly documented for future reference purposes. Data acquisition, physical components, shutdown devices, a control program, and the hydraulic system are all discussed in detail. Analysis is performed showing that the flow within the Mach 2 nozzle only reaches Mach 1.8 for a portion of the flow, but that this portion of the flow is relatively stable for a wide range of settling chamber pressures. It is concluded that the tunnel with the nozzle blocks used functions correctly

Revitalization and Initial Testing of a Blowdown Supersonic Wind Tunnel

The Supersonic tunnel located in Patterson Labs at Mississippi State University has been thoroughly documented for future reference purposes. Data acquisition, physical components, shutdown devices, a control program, and the hydraulic system are all discussed in detail. Analysis is performed showing that the flow within the Mach 2 nozzle only reaches Mach 1.8 for a portion of the flow, but that this portion of the flow is relatively stable for a wide range of settling chamber pressures. It is concluded that the tunnel with the nozzle blocks used functions correctly

Driving alkali Rydberg transitions with a phase-modulated optical lattice

We develop and demonstrate a spectroscopic method for Rydberg-Rydberg transitions using a phase-controlled and -modulated, standing-wave laser field focused on a cloud of cold $^{85}$Rb Rydberg atoms. The method is based on the ponderomotive (${\bf{A}}^2$) interaction of the Rydberg electron, which has less-restrictive selection rules than electric-dipole couplings, allowing us to probe both $nS_{1/2}\rightarrow nP_{1/2}$ and $nS_{1/2}\rightarrow (n+1)S_{1/2}$ transitions in first-order. Without any need to increase laser power, third and fourth-order sub-harmonic drives are employed to access Rydberg transitions in the 40 to 70 GHz frequency range using widely-available optical phase modulators in the Ku-band (12 to 18 GHz). Measurements agree well with simulations based on the model we develop. The spectra have prominent Doppler-free, Fourier-limited components. The method paves the way for optical Doppler-free high-precision spectroscopy of Rydberg-Rydberg transitions and for spatially-selective qubit manipulation with $\mu$m-scale resolution in Rydberg-based simulators and quantum computers

Rydberg-EIT of 85^{85}Rb vapor in a cell with Ne buffer gas

We investigate Rydberg electromagnetically induced transparency (EIT) of $^{85}$Rb atomic vapor in a glass cell that contains a 5-Torr neon buffer gas. At low probe power, EIT lines exhibit a positive frequency shift of about 70~MHz and a broadening of about 120~MHz, with minimal dependence on the principal quantum number of the Rydberg states. The EIT line shift arises from s-wave scattering between the Rydberg electron and the Ne atoms, which induces a positive shift near 190~MHz, and from the polarization of the Ne atoms within the Rydberg atom, which adds a negative shift near -120~MHz. The line broadening is largely due to the Ne polarization. Our experimental results are in good qualitative agreement with our theoretical model, in which the shift is linear in buffer-gas density. Our results suggest that Rydberg-EIT can serve as a direct spectroscopic probe for buffer-gas density at low pressure, and that it is suitable for non-invasive measurement of electric fields in low-pressure noble-gas discharge plasmas and in dusty plasmas

Active Prokaryotic Communities Along a Thermally and Geochemically Variable Transect in Guaymas Basin Hydrothermal Sediments

The microbial inhabitants of deep-sea vents are genetically and metabolically diverse, and often make a living at the edge of biological temperature limits. Guaymas Basin, a nascent spreading center in the Gulf of California, provides a unique environment in which to study prokaryotic communities across a range of thermal and geochemical niches. Unlike most vents, Guaymas is blanketed in thick sediments, ranging from 3ºC to 200+ºC within half a meter below the sea floor. Microbial mats, including one nicknamed "Megamat," serve as bull's-eyes for subsurface hydrothermal activity. Here we explore Megamat's subsurface, spanning low-temperature (3º), low-methane (0.3mM) to high-temperature (85º), high-methane (3+ mM) sediments, and the 16S rRNA-based phylogeny of active prokaryotes therein. Pyrosequencing revealed the fewest OTUs yet highest Shannon-Wiener diversity within the hottest sediments. Sequences of Sulfurimonas were nearly ubiquitous, and sequences from the heterotrophic MBGB dominated outside the mat's perimeter. Putative methane cyclers were most abundant within the methane-saturated mat center, including ANME-2c, Methermicoccaceae, Guaymas-specific ANME-1 groups, and a deeply-branching, novel group, "Guaymas Methanomicrobia." The expected Deltaproteobacterial sulfate reducers were not common in this survey; in fact Archaeoglobus and Thermodesulfobacteria sequences were recovered in exponentially higher abundance in the hottest sediments. Major groups were most similar outside of Megamat and at its edge, in contrast with strikingly core-specific communities in central mat samples. The mat's edge appears to be a transition zone hosting sequences found both in the central mat and in bare sediment, while the distinct community assemblages within central Megamat highlight horizontal and vertical variability in Guaymas Basin. Together, these data provide insights into community changes with temperature and substrates at high resolution over small spatial scales.Master of Scienc

Nuclear Charge Density Distributions from Elastic Electron Scattering Data

The model independent procedure of extracting charge density distributions from elastic electron scattering data is investigated. The charge density distributions are expanded on an orthonormal basis and the parameters of the expansions are fixed by the comparison with the experimental data. Two bases with different analytical properties (Fourier-Bessel and Hermite) are used. This allows us to disentangle the uncertainties coming from the choice of the expansion basis from those intrinsic to the extraction procedure. We design a set of tests to select the number of the expansion coefficients adequate for a proper description of the data. The procedure is applied to elastic data measured on $^{12}$C, $^{40}$Ca and $^{208}$Pb nuclei.Comment: 17 pages, 11 figures available on request to [email protected], to be published in Nucl.Phy

Electromagnetic Form Factors of the Nucleon and Compton Scattering

We review the experimental and theoretical status of elastic electron scattering and elastic low-energy photon scattering (with both real and virtual photons) from the nucleon. As a consequence of new experimental facilities and new theoretical insights, these subjects are advancing with unprecedented precision. These reactions provide many important insights into the spatial distributions and correlations of quarks in the nucleon.Comment: 47 pages, 18 figures, includes corrections and updates to published manuscrip