3,940 research outputs found
An Economic Analysis of a Drug-Selling Gang's Finances
We analyze a unique data set detailing the financial activities of a drug-selling street gang on a monthly basis over a four-year period in the recent past. The data, originally compiled by the gang leader to aid in managing the organization, contain detailed information on both the sources of revenues (e.g. drug sales, extortion) and expenditrues (e.g. costs of drugs sold, weapons, tribute to the central gang organization, wages paid to various levels of the gang). Street-level drug dealing appears to be less lucrative than is generally though. We estimate the average wage in the organization to rise from roughly 11 per hour over the time period studied. The distribution of wages, however, is extremely skewed. Gang leaders earn far more than they could in the legitimate sector, but the actual street-level dealers appear to earn less than the minimum wage throughout most of our sample, in spite of the substantial risks associated with such activities (the annual violent death rate in our sample is 0.07), There is some evidence consistent both with compensating differentials and efficiency wages. The markup on drugs suggests that the gang has substantial local market power. Gang wars appear to have an important strategic component: violence on another gang's turf shifts demand away from that area. The gang we observe responds to such attacks by pricing below marginal cost, suggesting either economic punishment for the rival gang or the presence of switching for users that makes market share maintenance valuable. We investigate a range of alternative methods for estimating the willingness of gang members to accept risks of death, all of which suggest that the implicit value that gang members place on their own lives is very low.
CP violating anomalous top-quark couplings at the LHC
We study the T odd correlations induced by CP violating anomalous top-quark
couplings at both production and decay level in the process gg --> t t_bar -->
(b mu+ nu_mu) (b_bar mu- nu_mu_bar). We consider several counting asymmetries
at the parton level and find the ones with the most sensitivity to each of
these anomalous couplings at the LHC.Comment: 14 LaTeX Pages, 1 EPS Figure, minor typos correcte
Segmentation of Moving Object with Uncovered Background, Temporary Poses and GMOB
AbstractVideo has to be segmented into objects for content-based processing. A number of video object segmentation algorithms have been proposed such as semiautomatic and automatic. Semiautomatic methods adds burden to users and also not suitable for some applications. Automatic segmentation systems are still a challenge, although they are required by many applications. The proposed work aims at contributing to identify the gaps that are present in the current segmentation system and also to give the possible solutions to overcome those gaps so that the accurate and efficient video segmentation system can be developed. The proposed system aims to resolve the issue of uncovered background, Temporary poses and Global motion of background
Preparation and decay of a single quantum of vibration at ambient conditions
A single quantum of excitation of a mechanical oscillator is a textbook
example of the principles of quantum physics. Mechanical oscillators, despite
their pervasive presence in nature and modern technology, do not generically
exist in an excited Fock state. In the past few years, careful isolation of
GHz-frequency nano-scale oscillators has allowed experimenters to prepare such
states at milli-Kelvin temperatures. These developments illustrate the tension
between the basic predictions of quantum mechanics that should apply to all
mechanical oscillators existing even at ambient conditions, and the complex
experiments in extreme conditions required to observe those predictions. We
resolve the tension by creating a single Fock state of a vibration mode of a
crystal at room temperature using a technique that can be applied to any
Raman-active system. After exciting a bulk diamond with a femtosecond laser
pulse and detecting a Stokes-shifted photon, the 40~THz Raman-active internal
vibrational mode is prepared in the Fock state with probability.
The vibrational state is read out by a subsequent pulse, which when subjected
to a Hanbury-Brown-Twiss intensity correlation measurement reveals the
sub-Poisson number statistics of the vibrational mode. By controlling the delay
between the two pulses we are able to witness the decay of the vibrational Fock
state over its ps lifetime at room temperature. Our technique is agnostic
to specific selection rules, and should thus be applicable to any Raman-active
medium, opening a new generic approach to the experimental study of quantum
effects related to vibrational degrees of freedom in molecules and solid-state
systems
Measurement and control of a mechanical oscillator at its thermal decoherence rate
In real-time quantum feedback protocols, the record of a continuous
measurement is used to stabilize a desired quantum state. Recent years have
seen highly successful applications in a variety of well-isolated
micro-systems, including microwave photons and superconducting qubits. By
contrast, the ability to stabilize the quantum state of a tangibly massive
object, such as a nanomechanical oscillator, remains a difficult challenge: The
main obstacle is environmental decoherence, which places stringent requirements
on the timescale in which the state must be measured. Here we describe a
position sensor that is capable of resolving the zero-point motion of a
solid-state, nanomechanical oscillator in the timescale of its thermal
decoherence, a critical requirement for preparing its ground state using
feedback. The sensor is based on cavity optomechanical coupling, and realizes a
measurement of the oscillator's displacement with an imprecision 40 dB below
that at the standard quantum limit, while maintaining an
imprecision-back-action product within a factor of 5 of the Heisenberg
uncertainty limit. Using the measurement as an error signal and radiation
pressure as an actuator, we demonstrate active feedback cooling (cold-damping)
of the 4.3 MHz oscillator from a cryogenic bath temperature of 4.4 K to an
effective value of 1.10.1 mK, corresponding to a mean phonon number of
5.30.6 (i.e., a ground state probability of 16%). Our results set a new
benchmark for the performance of a linear position sensor, and signal the
emergence of engineered mechanical oscillators as practical subjects for
measurement-based quantum control.Comment: 24 pages, 10 figures; typos corrected in main text and figure
Proximity-induced supercurrent through topological insulator based nanowires for quantum computation studies
Proximity induced superconducting energy gap in the surface states of
topological insulators has been predicted to host the much wanted Majorana
fermions for fault tolerant quantum computation. Recent theoretically proposed
architectures for topological quantum computation via Majoranas are based on
large networks of Kitaevs one dimensional quantum wires, which pose a huge
experimental challenge in terms of scalability of the current single nanowire
based devices. Here, we address this problem by realizing robust
superconductivity in junctions of fabricated topological insulator Bi2Se3
nanowires proximity coupled to conventional s wave superconducting W
electrodes. Milling technique possesses great potential in fabrication of any
desired shapes and structures at nanoscale level, and therefore can be
effectively utilized to scale up the existing single nanowire based design into
nanowire based network architectures. We demonstrate the dominant role of
ballistic topological surface states in propagating the long range proximity
induced superconducting order with high IcRN product in long Bi2Se3 junctions.
Large upper critical magnetic fields exceeding the Chandrasekhar Clogston limit
suggests the existence of robust superconducting order with spin triplet cooper
pairing. An unconventional inverse dependence of IcRN product on the width of
the nanowire junction was also observed.Comment: 12 page
Evidence of robust 2D transport and Efros-Shklovskii variable range hopping in disordered topological insulator (Bi2Se3) nanowires
We report the experimental observation of variable range hopping conduction
in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological
insulator (Bi2Se3). The value of the exponent in the hopping equation was
extracted as ~ 1/2 for different widths of nanowires, which is the proof of the
presence of Efros-Shklovskii hopping transport mechanism in a strongly
disordered system. High localization lengths (0.5nm, 20nm) were calculated for
the devices. A careful analysis of the temperature dependent fluctuations
present in the magnetoresistance curves, using the standard Universal
Conductance Fluctuation theory, indicates the presence of 2D topological
surface states. Also, the surface state contribution to the conductance was
found very close to one conductance quantum. We believe that our experimental
findings shed light on the understanding of quantum transport in disordered
topological insulator based nanostructures.Comment: 14pages, 4 figure
Effect of non-magnetic impurities on the magnetic states of anatase TiO
The electronic and magnetic properties of TiO, TiO,
TiON, and TiOF compounds have been studied
by using \emph{ab initio} electronic structure calculations. TiO is found
to evolve from a wide-band-gap semiconductor to a narrow-band-gap semiconductor
to a half-metallic state and finally to a metallic state with oxygen vacancy,
N-doping and F-doping, respectively. Present work clearly shows the robust
magnetic ground state for N- and F-doped TiO. The N-doping gives rise to
magnetic moment of 0.4 at N-site and 0.1 each at
two neighboring O-sites, whereas F-doping creates a magnetic moment of
0.3 at the nearest Ti atom. Here we also discuss the possible
cause of the observed magnetic states in terms of the spatial electronic charge
distribution of Ti, N and F atoms responsible for bond formation.Comment: 11 pages, 4 figures To appear J. Phys.: Condens. Matte
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