624 research outputs found
A cognitive -behavioral -based workshop intervention for perfectionism
Perfectionistic thinking, attitudes, beliefs, and behaviors can have negative influences on mental and physical health. Overly rigid and self-critical perfectionistic thinking also complicates treatment for people seeking to alleviate mental health and medical concerns. Several researchers have offered suggestions for treating perfectionism, but no empirical treatment studies with follow-up results have been published. Only DiBartolo, Frost, Dixon, and Almodovar (2001) conducted a brief manipulation of public speaking fears related to concern over mistakes and employed a control group. The current study expanded the research literature with the creation and evaluation of a 3-hour cognitive-behavioral workshop for perfectionism. The results indicate that this workshop was effective in specifically reducing maladaptive perfectionism, while also lowering depression and general distress ratings. Individuals with moderate and high pre-treatment levels of perfectionism maintained treatment gains at 3-week and 3-month follow-ups. Treatment gains in depression and general distress were maintained by women at 3-week and 3-month follow-ups while immediate treatment effects in men appeared to slightly rebound at 3-months. The workshop thus provided an effective, brief treatment intervention for perfectionism and related psychopathology. The workshop is expected to favorably apply to clinical populations and those referred specifically for maladaptive perfectionism treatment. Adaptations of the workshop might also be beneficial in targeting those at risk for maladaptive perfectionism such as individuals routinely exposed to high pressure performance situations
Perfectionism and the role of self-esteem
Over the past two decades, research interest has peaked in the specific study of perfectionism as a trait and risk factor for psychopathology, namely depression. This current study hypothesized that perfectionism\u27s impact on an individual\u27s mental health is mediated by that individual\u27s feelings of self-esteem. Research by Preusser, Rice, and Ashby (1994) and Rice, Ashby, and Slaney (1998) have noted evidence for this mediational relationship of self-esteem between perfectionism and depression. Using a sample of 189 undergraduate student volunteers (64 men and 125 women), results indicated that self-esteem was a significant mediator in the relationships between maladaptive perfectionism and depression, as well as anxiety and general distress. In relation to adaptive perfectionism, self-esteem was not a significant mediator, but may serve as a protective factor against adverse mental health outcomes. Thus, self-esteem appears to represent a critical determinant of perfectionism-related distress
Breaking a chaos-noise-based secure communication scheme
This paper studies the security of a secure communication scheme based on two
discrete-time intermittently-chaotic systems synchronized via a common random
driving signal. Some security defects of the scheme are revealed: 1) the key
space can be remarkably reduced; 2) the decryption is insensitive to the
mismatch of the secret key; 3) the key-generation process is insecure against
known/chosen-plaintext attacks. The first two defects mean that the scheme is
not secure enough against brute-force attacks, and the third one means that an
attacker can easily break the cryptosystem by approximately estimating the
secret key once he has a chance to access a fragment of the generated
keystream. Yet it remains to be clarified if intermittent chaos could be used
for designing secure chaotic cryptosystems.Comment: RevTeX4, 11 pages, 15 figure
Stochastic Gravitational Wave Measurements with Bar Detectors: Dependence of Response on Detector Orientation
The response of a cross-correlation measurement to an isotropic stochastic
gravitational-wave background depends on the observing geometry via the overlap
reduction function. If one of the detectors being correlated is a resonant bar
whose orientation can be changed, the response to stochastic gravitational
waves can be modulated. I derive the general form of this modulation as a
function of azimuth, both in the zero-frequency limit and at arbitrary
frequencies. Comparisons are made between pairs of nearby detectors, such as
LIGO Livingston-ALLEGRO, Virgo-AURIGA, Virgo-NAUTILUS, and EXPLORER-AURIGA,
with which stochastic cross-correlation measurements are currently being
performed, planned, or considered.Comment: 17 pages, REVTeX (uses rcs, amsmath, hyperref, and graphicx style
files), 4 figures (8 eps image files
Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst
We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large
Telescope (VLT), V- and R-band) observations of the intermediate mass black
hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show
that the V-band magnitudes vary with time, thus proving that a portion of the
observed emission originates in the accretion disk. Using the first quiescent
optical observations of HLX-1, we show that the stellar population surrounding
HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may
increase before the X-ray emission consistent with the scenario proposed by
Lasota et al. (2011) in which the regular outbursts could be related to the
passage at periastron of a star circling the intermediate mass black hole in an
eccentric orbit, which triggers mass transfer into a quasi-permanent accretion
disk around the black hole. Further, if there is indeed a delay in the X-ray
emission we estimate the mass-transfer delivery radius to be ~1e11 cm.Comment: 9 pages, 2 figures, accepted for publication in ApJ
Restless quiescence: thermonuclear flashes between transient X-ray outbursts
For thermonuclear flashes to occur on neutron-star surfaces, fuel must have
been accreted from a donor star. However, sometimes flashes are seen from
transient binary systems when they are thought to be in their quiescent phase,
during which no accretion, or relatively little, is expected to occur. We
investigate the accretion luminosity during several such flashes, including the
first-ever and brightest detected flash from Cen X-4 in 1969. We infer from
observations and theory that immediately prior to these flashes the accretion
rate must have been between about 0.001 and 0.01 times the equivalent of the
Eddington limit, which is roughly 2 orders of magnitude less than the peak
accretion rates seen in these transients during an X-ray outburst and 3-4
orders of magnitude more than the lowest measured values in quiescence.
Furthermore, three such flashes, including the one from Cen X-4, occurred
within 2 to 7 days followed by an X-ray outburst. A long-term episode of
enhanced, but low-level, accretion is predicted near the end of the quiescent
phase by the disk-instability model, and may thus have provided the right
conditions for these flashes to occur. We discuss the possibility of whether
these flashes acted as triggers of the outbursts, signifying a dramatic
increase in the accretion rate. Although it is difficult to rule out, we find
it unlikely that the irradiance by these flashes is sufficient to change the
state of the accretion disk in such a dramatic way.Comment: 9 pages, 3 figures, accepted for publication in A&A; referee comments
included plus improved text; results unchange
Three Additional Quiescent Low-Mass X-ray Binary Candidates in 47 Tucanae
We identify through their X-ray spectra one certain (W37) and two probable
(W17 and X4) quiescent low-mass X-ray binaries (qLMXBs) containing neutron
stars in a long Chandra X-ray exposure of the globular cluster 47 Tucanae, in
addition to the two previously known qLMXBs. W37's spectrum is dominated by a
blackbody-like component consistent with radiation from the hydrogen atmosphere
of a 10 km neutron star. W37's lightcurve shows strong X-ray variability which
we attribute to variations in its absorbing column depth, and eclipses with a
probable 3.087 hour period. For most of our exposures, W37's blackbody-like
emission (assumed to be from the neutron star surface) is almost completely
obscured, yet some soft X-rays (of uncertain origin) remain. Two additional
candidates, W17 and X4, present X-ray spectra dominated by a harder component,
fit by a power-law of photon index ~1.6-3. An additional soft component is
required for both W17 and X4, which can be fit with a 10 km hydrogen-atmosphere
neutron star model. X4 shows significant variability, which may arise from
either its power-law or hydrogen-atmosphere spectral component. Both W17 and X4
show rather low X-ray luminosities, Lx(0.5-10 keV)~5*10^{31} ergs/s. All three
candidate qLMXBs would be difficult to identify in other globular clusters,
suggesting an additional reservoir of fainter qLMXBs in globular clusters that
may be of similar numbers as the group of previously identified objects. The
number of millisecond pulsars inferred to exist in 47 Tuc is less than 10 times
larger than the number of qLMXBs in 47 Tuc, indicating that for typical
inferred lifetimes of 10 and 1 Gyr respectively, their birthrates are
comparable.Comment: Accepted for publication in ApJ. 13 pages, 7 figures (2 color
The origin of variability of the intermediate-mass black-hole ULX system HLX-1 in ESO 243-49
The ultra-luminous intermediate-mass black-hole system HLX-1 in the ESO
243-49 galaxy exhibits variability with a possible recurrence time of a few
hundred days. Finding the origin of this variability would constrain the still
largely unknown properties of this extraordinary object. Since it exhibits an
intensity-hardness behavior characteristic of black-hole X-ray transients, we
have analyzed the variability of HLX-1 in the framework of the disk instability
model that explains outbursts of such systems. We find that the long-term
variability of HLX-1 is unlikely to be explained by a model in which outbursts
are triggered by thermal-viscous instabilities in an accretion disc. Possible
alternatives include the instability in a radiation-pressure dominated disk but
we argue that a more likely explanation is a modulated mass-transfer due to
tidal stripping of a star on an eccentric orbit around the intermediate-mass
black hole. We consider an evolutionary scenario leading to the creation of
such a system and estimate the probability of its observation. We conclude,
using a simplified dynamical model of the post-collapse cluster, that no more
than 1/100 to 1/10 of Mbh < 10^4 Msun IMBHs - formed by run-away stellar
mergers in the dense collapsed cores of young clusters - could have a few times
1 Msun Main-Sequence star evolve to an AGB on an orbit eccentric enough for
mass transfer at periapse, while avoiding collisional destruction or being
scattered into the IMBH by 2-body encounters. The finite but low probability of
this configuration is consistent with the uniqueness of HLX-1. We note,
however, that the actual response of a standard accretion disk to bursts of
mass transfer may be too slow to explain the observations unless the orbit is
close to parabolic (and hence even rarer) and/or additional heating, presumably
linked to the highly time-dependent gravitational potential, are invoked.Comment: 8 pages, 2 figures. Additional figure, extended discussion. To be
published in ApJ, June 10, 2011, v734 -
A four-year baseline Swift study of enigmatic X-ray transients located near the Galactic center
We report on continued monitoring observations of the Galactic center carried
out by the X-ray telescope aboard the Swift satellite in 2008 and 2009. This
campaign revealed activity of the five known X-ray transients AX J1745.6-2901,
CXOGC J174535.5-290124, GRS 1741-2853, XMM J174457-2850.3 and CXOGC
J174538.0-290022. All these sources are known to undergo very faint X-ray
outbursts with 2-10 keV peak luminosities of Lx,peak~1E34-1E36 erg/s, although
the two confirmed neutron star low-mass X-ray binaries AX J1745.6-2901 and GRS
1741-2853 can also become brighter (Lx,peak~1E36-1E37 erg/s). We discuss the
observed long-term lightcurves and X-ray spectra of these five enigmatic
transients. In 2008, AX J1745.6-2901 returned to quiescence following an
unusually long accretion outburst of more than 1.5 years. GRS 1741-2853 was
active in 2009 and displayed the brightest outburst ever recorded for this
source, reaching up to a 2-10 keV luminosity of Lx~1E37 (D/7.2 kpc)^2 erg/s.
This system appears to undergo recurrent accretion outbursts approximately
every 2 years. Furthermore, we find that the unclassified transient XMM
J174457-2850.3 becomes bright only during short episodes (days) and is often
found active in between quiescence (Lx~1E32 erg/s) and its maximum outburst
luminosity of Lx~1E36 erg/s. CXOGC J174535.5-290124 and CXOGC J174538.0-290022,
as well as three other very-faint X-ray transients that were detected by Swift
monitoring observations in 2006, have very low time-averaged mass-accretion
rates of ~< 2E-12 Msun/yr. Despite having obtained two years of new data in
2008 and 2009, no new X-ray transients were detected.Comment: Minor textual revisions according to referee report, accepted for
publication in A&
Investigating slim disk solutions for HLX-1 in ESO 243-49
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the
best intermediate mass black hole candidate, displays spectral transitions
similar to those observed in Galactic black hole binaries, but with a
luminosity 100-1000 times higher. We investigated the X-ray properties of this
unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra
with a disk model computing spectra for a wide range of sub- and
super-Eddington accretion rates assuming a non-spinning black hole and a
face-on disk (i = 0 deg). Under these assumptions we find that the black hole
in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion
flow is in the sub-Eddington regime. The disk radiation efficiency is eta =
0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation
for our mass estimate. At the outburst peaks, the source radiates near the
Eddington limit. The accretion rate then stays constant around 4 x 10^(-4)
M_odot yr^(-1) for several days and then decreases exponentially. Such
"plateaus" in the accretion rate could be evidence that enhanced mass transfer
rate is the driving outburst mechanism in HLX-1. We also report on the new
outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this
new outburst further strengthens the ~1 year recurrence timescale.Comment: 24 pages, 10 figures, accepted for publication in Ap
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