25,193 research outputs found
Lipschitz shadowing implies structural stability
We show that the Lipschitz shadowing property of a diffeomorphism is
equivalent to structural stability. As a corollary, we show that an expansive
diffeomorphism having the Lipschitz shadowing property is Anosov.Comment: 11 page
Amplified Dispersive Fourier-Transform Imaging for Ultrafast Displacement Sensing and Barcode Reading
Dispersive Fourier transformation is a powerful technique in which the
spectrum of an optical pulse is mapped into a time-domain waveform using
chromatic dispersion. It replaces a diffraction grating and detector array with
a dispersive fiber and single photodetector. This simplifies the system and,
more importantly, enables fast real-time measurements. Here we describe a novel
ultrafast barcode reader and displacement sensor that employs
internally-amplified dispersive Fourier transformation. This technique
amplifies and simultaneously maps the spectrally encoded barcode into a
temporal waveform. It achieves a record acquisition speed of 25 MHz -- four
orders of magnitude faster than the current state-of-the-art.Comment: Submitted to a journa
Criminal social identity and suicide ideation among Pakistani young prisoners.
© Emerald Group Publishing Limited. Purpose: Suicidal behaviour is a common in prisoners, yet little is known about the factors that may protect against thoughts of ending one's life. The purpose of this paper is to specify and test a structural model to examine the relationship between three criminal social identity (CSI) dimensions (in-group affect, in-group ties, and cognitive centrality) and suicide ideation while controlling for period of confinement, age, criminal friends, and offense type (violent vs non-violent). Design/methodology/approach: Participants were 415 male juvenile offenders incarcerated in prisons in Khyber Pakhtunkhwa Pakistan. A structural model was specified and tested using Mplus to examine the relationships between the three factors of CSI and suicidal thoughts, while controlling for age, offender type, period of confinement, and substance dependence. Findings: The model provided an adequate fit for the data, explaining 22 per cent of variance in suicidal thoughts. In-group affect (the level of personal bonding with other criminals) was found to exert a strong protective effect against suicide ideation. Originality/value: The research contributes important information on suicide ideation in Pakistan, an Islamic country in which suicide is considered a sin and subsequently a criminal offence. Results indicate that Juvenile offenders' sense of shared identity may help to prevent the development of thoughts of death by suicide. Consequently, separating and isolating young prisoners may be ill advised
Latent classes of delinquent behaviour associated with criminal social identity among juvenile offenders in Pakistan
© Emerald Group Publishing Limited. Purpose â The purpose of this paper is to examine the number and nature of latent classes of delinquency that exist among male juvenile offenders incarcerated in prisons in Pakistan. Design/methodology/approach â The sample consisted of 415 young male offenders incarcerated in prisons in Khyber Pakhtunkhwa (KPK) Pakistan. Latent class analysis was employed to determine the number and nature of delinquency latent classes. Multinomial logistic regression was used to estimate the associations between latent classes and the three factors of criminal social identity (cognitive centrality, in-group affect, and in-group ties) whilst controlling for criminal friends, period of confinement, addiction, age, and location. Findings â The best fitting latent class model was a three-class solution. The classes were labelled: âminor delinquentsâ (the baseline/normative class; Class 3), âmajor delinquentsâ (Class 1), and âmoderate delinquentsâ (Class 2). Class membership was predicted by differing external variables. Specifically, Class 1 membership was related to having more criminal friends; while Class 2 membership was related to lower levels of in-group affect and higher levels of in-group ties. Practical implications â Findings are discussed in relation to refining current taxonomic arguments regarding the structure of delinquency and implications for prevention of juvenile delinquent behaviour. Originality/value â First, most previous studies have focused on school children, whereas, this paper focuses on incarcerated juvenile offenders. Second, this research includes delinquents from Pakistan, whereas, most previous research has examined delinquent behaviour in western cultures
Probing the Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope
The long gamma-ray burst (GRB) rate is essential for revealing the connection
between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at
high redshift provides a strong probe of star formation history in the early
universe. While hundreds of GRBs are observed by Swift, it remains difficult to
determine the intrinsic GRB rate due to the complex trigger algorithm of Swift.
Current studies usually approximate the Swift trigger algorithm by a single
detection threshold. However, unlike the previously flown GRB instruments,
Swift has over 500 trigger criteria based on photon count rate and additional
image threshold for localization. To investigate possible systematic biases and
explore the intrinsic GRB properties, we developed a program that is capable of
simulating all the rate trigger criteria and mimicking the image trigger
threshold. We use this program to search for the intrinsic GRB rate. Our
simulations show that adopting the complex trigger algorithm of Swift increases
the detection rate of dim bursts. As a result, we find that either the GRB rate
is much higher than previously expected at large redshift, or the luminosity
evolution is non-negligible. We will discuss the best results of the GRB rate
in our search, and their impact on the star-formation history.Comment: 6 pages, 3 figures, 7th Huntsville Gamma-Ray Burst Symposium, GRB
2013: paper 35 in eConf Proceedings C130414
Transformation of stimulus correlations by the retina
Redundancies and correlations in the responses of sensory neurons seem to
waste neural resources but can carry cues about structured stimuli and may help
the brain to correct for response errors. To assess how the retina negotiates
this tradeoff, we measured simultaneous responses from populations of ganglion
cells presented with natural and artificial stimuli that varied greatly in
correlation structure. We found that pairwise correlations in the retinal
output remained similar across stimuli with widely different spatio-temporal
correlations including white noise and natural movies. Meanwhile, purely
spatial correlations tended to increase correlations in the retinal response.
Responding to more correlated stimuli, ganglion cells had faster temporal
kernels and tended to have stronger surrounds. These properties of individual
cells, along with gain changes that opposed changes in effective contrast at
the ganglion cell input, largely explained the similarity of pairwise
correlations across stimuli where receptive field measurements were possible.Comment: author list corrected in metadat
Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope
The gamma-ray burst (GRB) rate is essential for revealing the connection
between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at
high redshift provides a strong probe of star formation history in the early
universe. While hundreds of GRBs are observed by Swift, it remains difficult to
determine the intrinsic GRB rate due to the complex trigger algorithm of Swift.
Current studies of the GRB rate usually approximate the Swift trigger algorithm
by a single detection threshold. However, unlike the previously flown GRB
instruments, Swift has over 500 trigger criteria based on photon count rate and
additional image threshold for localization. To investigate possible systematic
biases and explore the intrinsic GRB properties, we develop a program that is
capable of simulating all the rate trigger criteria and mimicking the image
threshold. Our simulations show that adopting the complex trigger algorithm of
Swift increases the detection rate of dim bursts. As a result, our simulations
suggest bursts need to be dimmer than previously expected to avoid
over-producing the number of detections and to match with Swift observations.
Moreover, our results indicate that these dim bursts are more likely to be high
redshift events than low-luminosity GRBs. This would imply an even higher
cosmic GRB rate at large redshifts than previous expectations based on
star-formation rate measurements, unless other factors, such as the luminosity
evolution, are taken into account. The GRB rate from our best result gives a
total number of 4571^{+829}_{-1584} GRBs per year that are beamed toward us in
the whole universe.
SPECIAL NOTE (2015.05.16): This new version incorporates an erratum. All the
GRB rate normalizations () should be a factor of 2 smaller
than previously reported. Please refer to the Appendix for more details. We
sincerely apologize for the mistake.Comment: 52 pages, 17 figures, published in ApJ 783, 24L (2014). An erratum is
included. A typo in Eq. 8 is fixed in this versio
Mapping isoprene emissions over North America using formaldehyde column observations from space
We present a methodology for deriving emissions of volatile organic compounds (VOC) using space-based column observations of formaldehyde (HCHO) and apply it to data from the Global Ozone Monitoring Experiment (GOME) satellite instrument over North America during July 1996. The HCHO column is related to local VOC emissions, with a spatial smearing that increases with the VOC lifetime. Isoprene is the dominant HCHO precursor over North America in summer, and its lifetime (â1 hour) is sufficiently short that the smearing can be neglected. We use the Goddard Earth Observing System global 3-D model of tropospheric chemistry (GEOS-CHEM) to derive the relationship between isoprene emissions and HCHO columns over North America and use these relationships to convert the GOME HCHO columns to isoprene emissions. We also use the GEOS-CHEM model as an intermediary to validate the GOME HCHO column measurements by comparison with in situ observations. The GEOS-CHEM model including the Global Emissions Inventory Activity (GEIA) isoprene emission inventory provides a good simulation of both the GOME data (r2 = 0.69, n = 756, bias = +11%) and the in situ summertime HCHO measurements over North America (r2 = 0.47, n = 10, bias = â3%). The GOME observations show high values over regions of known high isoprene emissions and a day-to-day variability that is consistent with the temperature dependence of isoprene emission. Isoprene emissions inferred from the GOME data are 20% less than GEIA on average over North America and twice those from the U.S. EPA Biogenic Emissions Inventory System (BEIS2) inventory. The GOME isoprene inventory when implemented in the GEOS-CHEM model provides a better simulation of the HCHO in situ measurements than either GEIA or BEIS2 (r2 = 0.71, n = 10, bias = â10%)
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