Particle Physics Implications for CoGeNT, DAMA, and Fermi

Recent results from the CoGeNT collaboration (as well as the annual modulation reported by DAMA/LIBRA) point toward dark matter with a light (5-10 GeV) mass and a relatively large elastic scattering cross section with nucleons (\sigma ~ 10^{-40} cm^2). In order to possess this cross section, the dark matter must communicate with the Standard Model through mediating particles with small masses and/or large couplings. In this Letter, we explore with a model independent approach the particle physics scenarios that could potentially accommodate these signals. We also discuss how such models could produce the gamma rays from the Galactic Center observed in the data of the Fermi Gamma Ray Space Telescope. We find multiple particle physics scenarios in which each of these signals can be accounted for, and in which the dark matter can be produced thermally in the early Universe with an abundance equal to the measured cosmological density.Comment: 4 pages, 2 figure

Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta_2O_5)

Amorphous tantala (a-Ta_2O_5) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta_2O_5 coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta 2O5 and other a-T_2O_5 studies

Neuronal Recordings with Solid-Conductor Intracellular Nanoelectrodes (SCINEs)

<div><p>Direct electrical recording of the neuronal transmembrane potential has been crucial to our understanding of the biophysical mechanisms subserving neuronal computation. Existing intracellular recording techniques, however, limit the accuracy and duration of such measurements by changing intracellular biochemistry and/or by damaging the plasma membrane. Here we demonstrate that nanoengineered electrodes can be used to record neuronal transmembrane potentials in brain tissue without causing these physiological perturbations. Using focused ion beam milling, we have fabricated Solid-Conductor Intracellular NanoElectrodes (SCINEs), from conventional tungsten microelectrodes. SCINEs have tips that are <300 nm in diameter for several micrometers, but can be easily handled and can be inserted into brain tissue. Performing simultaneous whole-cell patch recordings, we show that SCINEs can record action potentials (APs) as well as slower, subthreshold neuronal potentials without altering cellular properties. These results show a key role for nanotechnology in the development of new electrical recording techniques in neuroscience.</p> </div

SCINE and manipulator design.

<p><b>A</b>. Magnified cross-sectional drawing of the SCINE tip. <b>B</b> SCINE overview showing the pulled glass capillary and the gold pin for the electrical connection to the amplifier. <b>C</b> Scanning electron microscopy image using the backscattered electron detector for material contrast (metal vs. insulator). Width dimension  =  300 nm.</p

SCINEs can record both APs and slower, subthreshold potentials.

<p>SCINE recording (red) of subthreshold and suprathreshold signals evoked by a simultaneous whole-cell recording electrode (black). In the far right trace, the AP height and depolarizing step response are 109 mV and 27 mV above RMP, respectively. The SCINE recording measures 2.62 mV and 0.25 mV for the same features; the RMS of the noise in the first 100 ms of the SCINE recording (before current injection) is 0.05 mV. All traces shown are single, unaveraged traces that are low-pass filtered at 5 kHz. SCINE recordings are corrected for baseline drift.</p

SCINEs can be inserted into cells non-invasively.

<p>Examples (n = 5) where SCINE recordings did not significantly alter cellular properties (measured from whole-cell electrode). Comparison of input resistance, membrane potential and AP half width as measured with the whole-cell electrode before and after SCINE membrane penetration (error bars are 1 standard deviation). Overall means were: R_inp = 160±12 MΩ (mean ± s.d., before), 157±14 MΩ (after), p = 0.53 (paired t-test); V_m =  −67.3±0.8 mV; 68.3±0.7 mV; p = 0.31; APHW  =  2.11±0.11 ms; 2.13±0.09 ms; p = 0.64.</p

SCINE recording.

<p><b>A</b>. (left) Differential Interference Contrast (DIC) Micrograph of a patch-clamped neuron with the nanoelectrode above the focal plane. (right) Double recording from the same neuron after the SCINE is inserted into the patch-clamped neuron. <b>B</b> Simultaneous whole-cell patch (black) and SCINE (red) recording from a pyramidal neuron in a rat hippocampal slice culture. The red arrow indicates when the SCINE penetrated the neuronal membrane. Action potentials (APs) were evoked via the whole-cell electrode. Gaps between traces are approximately 100 msec. <b>C</b> Comparison of evoked action potentials in whole-cell and SCINE channel before (left) and after (right) membrane penetration by the SCINE. All traces shown are single, unaveraged traces that are low-pass filtered at 5 kHz. SCINE recordings are corrected for baseline drift.</p

Mechanical Model of Vertical Nanowire Cell Penetration

Direct access into cells’ interiors is essential for biomolecular delivery, gene transfection, and electrical recordings yet is challenging due to the cell membrane barrier. Recently, molecular delivery using vertical nanowires (NWs) has been demonstrated for introducing biomolecules into a large number of cells in parallel. However, the microscopic understanding of how and when the nanowires penetrate cell membranes is still lacking, and the degree to which actual membrane penetration occurs is controversial. Here we present results from a mechanical continuum model of elastic cell membrane penetration through two mechanisms, namely through “impaling” as cells land onto a bed of nanowires, and through “adhesion-mediated” penetration, which occurs as cells spread on the substrate and generate adhesion force. Our results reveal that penetration is much more effective through the adhesion mechanism, with NW geometry and cell stiffness being critically important. Stiffer cells have higher penetration efficiency, but are more sensitive to NW geometry. These results provide a guide to designing nanowires for applications in cell membrane penetration