The photoelectric effect without photons

Mathematical model of photoelectric effect without photon

Build-up of laser oscillations from quantum noise

Laser oscillation build up from quantum nois

A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy

Modern materials science requires efficient processing and characterization techniques for low dimensional systems. Raman spectroscopy is an important non-destructive tool, which provides enormous information on these materials. This understanding is not only interesting in its own right from a physicist's point of view, but can also be of considerable importance in optoelectronics and device applications of these materials in nanotechnology. The commercial Raman spectrometers are quite expensive. In this article, we have presented a relatively less expensive set-up with home-built collection optics attachment. The details of the instrumentation have been described. Studies on four classes of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of use in teaching and research on nanomaterials.Comment: 32 pages, 13 figure

Formation of Box Canyon, Idaho, by megaflood: implications for seepage erosion on Earth and Mars

Amphitheater- headed canyons have been used as diagnostic indicators of erosion by groundwater seepage, which has important implications for landscape evolution on Earth and astrobiology on Mars. Of perhaps any canyon studied, Box Canyon, Idaho, most strongly meets the proposed morphologic criteria for groundwater sapping because it is incised into a basaltic plain with no drainage network upstream, and approximately 10 cubic meters per second of seepage emanates from its vertical headwall. However, sediment transport constraints, ^4He and ^14C dates, plunge pools, and scoured rock indicate that a megaflood (greater than 220 cubic meters per second) carved the canyon about 45,000 years ago. These results add to a growing recognition of Quaternary catastrophic flooding in the American northwest, and may imply that similar features on Mars also formed by floods rather than seepage erosion

Operative versus non-operative treatment for closed, displaced, intra-articular fractures of the calcaneus : randomised controlled trial

Objective: To investigate whether surgery by open reduction and internal fixation provides benefit compared with non-operative treatment for displaced, intra-articular calcaneal fractures. Design: Pragmatic, multicentre, two arm, parallel group, assessor blinded randomised controlled trial (UK Heel Fracture Trial). Setting: 22 tertiary referral hospitals, United Kingdom. Participants: 151 patients with acute displaced intra-articular calcaneal fractures randomly allocated to operative (n=73) or non-operative (n=78) treatment. Main outcome measures: The primary outcome measure was patient reported Kerr-Atkins score for pain and function (scale 0-100, 100 being the best possible score) at two years after injury. Secondary outcomes were complications; hindfoot pain and function (American Orthopaedic Foot and Ankle Society score); general health (SF-36); quality of life (EQ-5D); clinical examination; walking speed; and gait symmetry. Analysis was by intention to treat. Results: 95% follow-up was achieved for the primary outcome (69 in operative group and 74 in non-operative group), and a complete set of secondary outcomes were available for 75% of participants. There was no significant difference in the primary outcome (mean Kerr-Atkins score 69.8 in operative group v 65.7 in non-operative group; adjusted 95% confidence interval of difference −7.1 to 7.0) or in any of the secondary outcomes between treatment groups. Complications and reoperations were more common in those who received operative care (estimated odds ratio 7.5, 95% confidence interval 2.0 to 41.8). Conclusions: Operative treatment compared with non-operative care showed no symptomatic or functional advantage after two years in patients with typical displaced intra-articular fractures of the calcaneus, and the risk of complications was higher after surgery. Based on these findings, operative treatment by open reduction and internal fixation is not recommended for these fractures

A Sample of OB Stars That Formed in the Field

We present a sample of 14 OB stars in the Small Magellanic Cloud that meet strong criteria for having formed under extremely sparse star-forming conditions in the field. These stars are a minimum of 28 pc in projection from other OB stars, and they are centered within symmetric, round HII regions. They show no evidence of bow shocks, implying that the targets are not transverse runaway stars. Their radial velocities relative to local HI also indicate that they are not line-of-sight runaway stars. A friends-of-friends analysis shows that 9 of the objects present a few low-mass companion stars, with typical mass ratios for the two highest-mass stars of around 0.1. This further substantiates that these OB stars formed in place, and that they can and do form in extremely sparse conditions. This poses strong constraints on theories of star formation and challenges proposed relations between cluster mass and maximum stellar mass.Comment: Accepted to ApJ, 12 page

Slip in the 2010–2011 Canterbury earthquakes, New Zealand

The 3rd September 2010 Mw 7.1 Darfield and 21st February 2011 Mw 6.3 Christchurch (New Zealand) earthquakes occurred on previously unknown faults. We use InSAR ground displacements, SAR amplitude offsets, field mapping, aerial photographs, satellite optical imagery, a LiDAR DEM and teleseismic body-wave modeling to constrain the pattern of faulting in these earthquakes. The InSAR measurements reveal slip on multiple strike-slip segments and secondary reverse faults associated with the Darfield main shock. Fault orientations are consistent with those expected from the GPS-derived strain field. The InSAR line-of-sight displacement field indicates the main fault rupture is about 45 km long, and is confined largely to the upper 10 km of the crust. Slip on the individual fault segments of up to 8 m at 4 km depth indicate stress drops of 6–10 MPa. In each event, rupture initiated on a reverse fault segment, before continuing onto a strike-slip segment. The non-double couple seismological moment tensors for each event are matched well by the sum of double couple equivalent moment tensors for fault slip determined by InSAR. The slip distributions derived from InSAR observations of both the Darfield and Christchurch events show a 15-km-long gap in fault slip south-west of Christchurch, which may present a continuing seismic hazard if a further unknown fault structure of significant size should exist there

On linearization of super sine-Gordon equation

Two sets of super Riccati equations are presented which result in two linear problems of super sine-Gordon equation. The linear problems are then shown to be related to each other by a super gauge transformation and to the super B\"{a}cklund transformation of the equation.Comment: 9 Page

Stability of the Magnetopause of Disk-Accreting Rotating Stars

We discuss three modes of oscillation of accretion disks around rotating magnetized neutron stars which may explain the separations of the kilo-Hertz quasi periodic oscillations (QPO) seen in low mass X-ray binaries. The existence of these compressible, non-barotropic magnetohydrodynamic (MHD) modes requires that there be a maximum in the angular velocity $\Omega_\phi(r)$ of the accreting material larger than the angular velocity of the star $\Omega_*$, and that the fluid is in approximately circular motion near this maximum rather than moving rapidly towards the star or out of the disk plane into funnel flows. Our MHD simulations show this type of flow and $\Omega_\phi(r)$ profile. The first mode is a Rossby wave instability (RWI) mode which is radially trapped in the vicinity of the maximum of a key function $g(r){\cal F}(r)$ at $r_{R}$. The real part of the angular frequency of the mode is $\omega_r=m\Omega_\phi(r_{R})$, where $m=1,2...$ is the azimuthal mode number. The second mode, is a mode driven by the rotating, non-axisymmetric component of the star's magnetic field. It has an angular frequency equal to the star's angular rotation rate $\Omega_*$. This mode is strongly excited near the radius of the Lindblad resonance which is slightly outside of $r_R$. The third mode arises naturally from the interaction of flow perturbation with the rotating non-axisymmetric component of the star's magnetic field. It has an angular frequency $\Omega_*/2$. We suggest that the first mode with $m=1$ is associated with the upper QPO frequency, $\nu_u$; that the nonlinear interaction of the first and second modes gives the lower QPO frequency, $\nu_\ell =\nu_u-\nu_*$; and that the nonlinear interaction of the first and third modes gives the lower QPO frequency $\nu_\ell=\nu_u-\nu_*/2$, where $\nu_*=\Omega_*/2\pi$.Comment: 10 pages, 7 figure

Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model

We suggest that the energy source of the observed diffuse gamma-ray emission from the direction of the Galactic center is the Galactic black hole Sgr A*, which becomes active when a star is captured at a rate of $\sim 10^{-5}$ yr^{-1}. Subsequently the star is tidally disrupted and its matter is accreted into the black hole. During the active phase relativistic protons with a characteristic energy $\sim 6\times 10^{52}$ erg per capture are ejected. Over 90% of these relativistic protons disappear due to proton-proton collisions on a timescale $\tau_{pp} \sim 10^4$ years in the small central bulge region with radius $\sim 50$ pc within Sgr A*, where the density is $\ge 10^3$ cm^{-3}. The gamma-ray intensity, which results from the decay of neutral pions produced by proton-proton collisions, decreases according to $e^{-t/\tau_{pp}}$, where t is the time after last stellar capture. Less than 5% of relativistic protons escaped from the central bulge region can survive and maintain their energy for >10^7 years due to much lower gas density outside, where the gas density can drop to $\sim 1$ cm$^{-3}$. They can diffuse to a $\sim 500$ pc region before disappearing due to proton-proton collisions. The observed diffuse GeV gamma-rays resulting from the decay of neutral pions produced via collision between these escaped protons and the gas in this region is expected to be insensitive to time in the multi-injection model with the characteristic injection rate of 10^{-5} yr^{-1}. Our model calculated GeV and 511 keV gamma-ray intensities are consistent with the observed results of EGRET and INTEGRAL, however, our calculated inflight annihilation rate cannot produce sufficient intensity to explain the COMPTEL data.Comment: 8 pages, 3 figures, accepted by A&