The Apollo Virtual Microscope Collection: Lunar Mineralogy and Petrology of Apollo 11, 12, 14, 15 and 16 Rocks

We report on the new Virtual Microscopes on Apollo 16 lunar samples in our Apollo Virtual Microscope collection

Tunneling Ionization Rates from Arbitrary Potential Wells

We present a practical numerical technique for calculating tunneling ionization rates from arbitrary 1-D potential wells in the presence of a linear external potential by determining the widths of the resonances in the spectral density, rho(E), adiabatically connected to the field-free bound states. While this technique applies to more general external potentials, we focus on the ionization of electrons from atoms and molecules by DC electric fields, as this has an important and immediate impact on the understanding of the multiphoton ionization of molecules in strong laser fields.Comment: 13 pages, 7 figures, LaTe

A multi-object spectral imaging instrument

We have developed a snapshot spectral imaging system which fits onto the side camera port of a commercial inverted microscope. The system provides spectra, in real time, from multiple points randomly selected on the microscope image. Light from the selected points in the sample is directed from the side port imaging arm using a digital micromirror device to a spectrometer arm based on a dispersing prism and CCD camera. A multi-line laser source is used to calibrate the pixel positions on the CCD for wavelength. A CMOS camera on the front port of the microscope allows the full image of the sample to be displayed and can also be used for particle tracking, providing spectra of multiple particles moving in the sample. We demonstrate the system by recording the spectra of multiple fluorescent beads in aqueous solution and from multiple points along a microscope sample channel containing a mixture of red and blue dye

Non-invasive, near-field terahertz imaging of hidden objects using a single pixel detector

Terahertz (THz) imaging has the ability to see through otherwise opaque materials. However, due to the long wavelengths of THz radiation ({\lambda}=300{\mu}m at 1THz), far-field THz imaging techniques are heavily outperformed by optical imaging in regards to the obtained resolution. In this work we demonstrate near-field THz imaging with a single-pixel detector. We project a time-varying optical mask onto a silicon wafer which is used to spatially modulate a pulse of THz radiation. The far-field transmission corresponding to each mask is recorded by a single element detector and this data is used to reconstruct the image of an object placed on the far side of the silicon wafer. We demonstrate a proof of principal application where we image a printed circuit board on the underside of a 115{\mu}m thick silicon wafer with ~100{\mu}m ({\lambda}/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity provided by the THz probe frequencies, we show that it is possible to detect fissures in the circuitry wiring of a few microns in size. Imaging systems of this type could have other uses where non-invasive measurement or imaging of concealed structures with high resolution is necessary, such as in semiconductor manufacturing or in bio-imaging

Luminosity Evolution of Early-type Galaxies to z=0.83: Constraints on Formation Epoch and Omega

We present deep spectroscopy with the Keck telescope of eight galaxies in the luminous X-ray cluster MS1054-03 at z=0.83. The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data to measure their structural parameters. Six galaxies have early-type spectra, and two have "E+A" spectra. The galaxies with early-type spectra define a tight Fundamental Plane (FP) relation. The evolution of the mass-to-light ratio is derived from the FP. The M/L ratio evolves as \Delta log M/L_B \propto -0.40 z (Omega_m=0.3, Omega_Lambda=0). The observed evolution of the M/L ratio provides a combined constraint on the formation redshift of the stars, the IMF, and cosmological parameters. For a Salpeter IMF (x=2.35) we find that z_form>2.8 and Omega_m<0.86 with 95% confidence. The constraint on the formation redshift is weaker if Omega_Lambda>0: z_form>1.7 if Omega_m=0.3 and Omega_Lambda=0.7. At present the limiting factor in constraining z_form and Omega from the observed luminosity evolution of early-type galaxies is the poor understanding of the IMF. We find that if Omega_m=1 the IMF must be significantly steeper than the Salpeter IMF (x>2.6).Comment: To be published in ApJ Letters, Volume 504, September 1, 1998. 5 pages, 4 figure

Fallback accretion on to a newborn magnetar : long GRBs with giant X-ray flares

Flares in the X-ray afterglow of gamma-ray bursts (GRBs) share more characteristics with the prompt emission than the afterglow, such as pulse profile and contained fluence. As a result, they are believed to originate from late-time activity of the central engine and can be used to constrain the overall energy budget. In this paper, we collect a sample of 19 long GRBs observed by Swift-XRT that contain giant flares in their X-ray afterglows. We fit this sample with a version of the magnetar propeller model, modified to include fallback accretion. This model has already successfully reproduced extended emission in short GRBs. Our best fits provide a reasonable morphological match to the light curves. However, 16 out of 19 of the fits require efficiencies for the propeller mechanism that approach 100%. The high efficiency parameters are a direct result of the high energy contained in the flares and the extreme duration of the dipole component, which forces either slow spin periods or low magnetic fields. We find that even with the inclusion of significant fallback accretion, in all but a few cases it is energetically challenging to produce prompt emission, afterglow and giant flares within the constraints of the rotational energy budget of a magnetar