5,782 research outputs found
An electron Talbot interferometer
The Talbot effect, in which a wave imprinted with transverse periodicity
reconstructs itself at regular intervals, is a diffraction phenomenon that
occurs in many physical systems. Here we present the first observation of the
Talbot effect for electron de Broglie waves behind a nanofabricated
transmission grating. This was thought to be difficult because of Coulomb
interactions between electrons and nanostructure gratings, yet we were able to
map out the entire near-field interference pattern, the "Talbot carpet", behind
a grating. We did this using a Talbot interferometer, in which Talbot
interference fringes from one grating are moire'-filtered by a 2nd grating.
This arrangement has served for optical, X-ray, and atom interferometry, but
never before for electrons. Talbot interferometers are particularly sensitive
to distortions of the incident wavefronts, and to illustrate this we used our
Talbot interferometer to measure the wavefront curvature of a weakly focused
electron beam. Here we report how this wavefront curvature demagnified the
Talbot revivals, and we discuss applications for electron Talbot
interferometers.Comment: 5 pages, 5 figures, updated version with abstrac
Integrated digital/electric aircraft concepts study
The integrated digital/electrical aircraft (IDEA) is an aircraft concept which employs all electric secondary power systems and advanced digital flight control systems. After trade analysis, preferred systems were applied to the baseline configuration. An additional configuration, the alternate IDEA, was also considered. For this concept the design ground rules were relaxed in order to quantify additional synergistic benefits. It was proposed that an IDEA configuration and technical risks associated with the IDEA systems concepts be defined and the research and development required activities to reduce these risks be identified. The selected subsystems include: power generation, power distribution, actuators, environmental control system and flight controls systems. When the aircraft was resized, block fuel was predicted to decrease by 11.3 percent, with 7.9 percent decrease in direct operating cost. The alternate IDEA shows a further 3.4 percent reduction in block fuel and 3.1 percent reduction in direct operating cost
Possible Signature of Low Scale Gravity in Ultra High Enegry Cosmic Rays
We show that the existence of low scale gravity at TeV scale could lead to a
direct production of photons with energies above 10^22 eV due to annihilation
of ultra high energy neutrinos on relic massive neutrinos of the galactic halo.
Air showers initialized in the terrestrial atmosphere by these ultra energetic
photons could be collected in near future by the new generation of cosmic ray
experiments.Comment: 5 pages, 3 figure
On the Origin of the Highest Energy Cosmic Rays
We present the results of a new estimation of the photodisintegration and
propagation of ultrahigh energy cosmic ray (UHCR) nuclei in intergalactic
space. The critical interactions for photodisintegration and energy loss of
UHCR nuclei occur with photons of the infrared background radiation (IBR). We
have reexamined this problem making use of a new determination of the IBR based
on empirical data, primarily from IRAS galaxies, and also collateral
information from TeV gamma-ray observations of two nearby BL Lac objects. Our
results indicate that a 200 EeV Fe nucleus can propagate apx. 100 Mpc through
the IBR. We argue that it is possible that the highest energy cosmic rays
observed may be heavy nuclei.Comment: 2 pages revtex with one figure, submitted to Physical Review Letter
Spectropolarimetric observations of Herbig Ae/Be Stars I: HiVIS spectropolarimetric calibration and reduction techniques
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope in Hawaii, we are collecting a large number of high precision
spectropolarimetrc observations of stars. In order to precisely measure very
small polarization changes, we have performed a number of polarization
calibration techniques on the AEOS telescope and HiVIS spectrograph. We have
extended our dedicated IDL reduction package and have performed some hardware
upgrades to the instrument. We have also used the ESPaDOnS spectropolarimeter
on CFHT to verify the HiVIS results with back-to-back observations of MWC 361
and HD163296. Comparision of this and other HiVIS data with stellar
observations from the ISIS and WW spectropolarimeters in the literature further
shows the usefulness of this instrument.Comment: 35 pages, 44 figures, Accepted by PAS
Observations of the J = 2 → 1 line of carbon monoxide in the NGC 2024 nebula
Observations have been made of the J = 2 → 1 transition of 12CO and 13CO in the molecular cloud near NGC 2024. The most intense emission comes from the central regions of the nebula close to areas of high optical extinction. The source contains two hotspots, but no significant velocity gradient or line-broadening was observed. This is consistent with a model in which the emission arises mainly from the high-density interface between the expanding HII region and a neutral cloud. Measurements of the 13CO isotope indicates that τ13 > 1.7, but there is insufficient information to derive the density in the region. Analysis of data for Mon R2, however, using the radially collapsing cloud model, indicates a hydrogen density of ~2 × 104 cm-3 for that source
Galactic Anisotropy as Signature of ``Top-Down'' Mechanisms of Ultra-High Energy Cosmic Rays
We show that ``top-down'' mechanisms of Ultra-High Energy Cosmic Rays which
involve heavy relic particle-like objects predict Galactic anisotropy of
highest energy cosmic rays at the level of minimum . This anisotropy
is large enough to be either observed or ruled out in the next generation of
experiments.Comment: 8 pages, 1 figure, LaTeX. Final version appeared in Pisma Zh. Eksp.
Teor. Fi
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