883 research outputs found
Results from the Blazar Monitoring Campaign at the Whipple 10m Gamma-ray Telescope
In September 2005, the observing program of the Whipple 10 m gamma-ray
telescope was redefined to be dedicated almost exclusively to AGN monitoring.
Since then the five Northern Hemisphere blazars that had already been detected
at Whipple are monitored routinely each night that they are visible. Thanks to
the efforts of a large number of multiwavelength collaborators, the first year
of this program has been very successful. We report here on the analysis of
Markarian 421 observations taken from November, 2005 to May, 2006 in the
gamma-ray, X-ray, optical and radio bands.Comment: 4 pages; contribution to the 30th International Cosmic Ray
Conference, Merida, Mexico, July 200
Inertial forces and the foundations of optical geometry
Assuming a general timelike congruence of worldlines as a reference frame, we
derive a covariant general formalism of inertial forces in General Relativity.
Inspired by the works of Abramowicz et. al. (see e.g. Abramowicz and Lasota,
Class. Quantum Grav. 14 (1997) A23), we also study conformal rescalings of
spacetime and investigate how these affect the inertial force formalism. While
many ways of describing spatial curvature of a trajectory has been discussed in
papers prior to this, one particular prescription (which differs from the
standard projected curvature when the reference is shearing) appears novel. For
the particular case of a hypersurface-forming congruence, using a suitable
rescaling of spacetime, we show that a geodesic photon is always following a
line that is spatially straight with respect to the new curvature measure. This
fact is intimately connected to Fermat's principle, and allows for a certain
generalization of the optical geometry as will be further pursued in a
companion paper (Jonsson and Westman, Class. Quantum Grav. 23 (2006) 61). For
the particular case when the shear-tensor vanishes, we present the inertial
force equation in three-dimensional form (using the bold face vector notation),
and note how similar it is to its Newtonian counterpart. From the spatial
curvature measures that we introduce, we derive corresponding covariant
differentiations of a vector defined along a spacetime trajectory. This allows
us to connect the formalism of this paper to that of Jantzen et. al. (see e.g.
Bini et. al., Int. J. Mod. Phys. D 6 (1997) 143).Comment: 42 pages, 7 figure
Current-voltage scaling of a Josephson-junction array at irrational frustration
Numerical simulations of the current-voltage characteristics of an ordered
two-dimensional Josephson junction array at an irrational flux quantum per
plaquette are presented. The results are consistent with an scaling analysis
which assumes a zero temperature vortex glass transition. The thermal
correlation length exponent characterizing this transition is found to be
significantly different from the corresponding value for vortex-glass models in
disordered two-dimensional superconductors. This leads to a current scale where
nonlinearities appear in the current-voltage characteristics decreasing with
temperature roughly as in contrast with the behavior expected
for disordered models.Comment: RevTex 3.0, 12 pages with Latex figures, to appear in Phys. Rev. B
54, Rapid. Com
Hyperbolic shear polaritons in low-symmetry crystals
The lattice symmetry of a crystal is one of the most important factors in determining its physical properties. Particularly, low-symmetry crystals offer powerful opportunities to control light propagation, polarization and phase. Materials featuring extreme optical anisotropy can support a hyperbolic response, enabling coupled light–matter interactions, also known as polaritons, with highly directional propagation and compression of light to deeply sub-wavelength scales. Here we show that monoclinic crystals can support hyperbolic shear polaritons, a new polariton class arising in the mid-infrared to far-infrared due to shear phenomena in the dielectric response. This feature emerges in materials in which the dielectric tensor cannot be diagonalized, that is, in low-symmetry monoclinic and triclinic crystals in which several oscillators with non-orthogonal relative orientations contribute to the optical response. Hyperbolic shear polaritons complement previous observations of hyperbolic phonon polaritons in orthorhombic and hexagonal crystal systems, unveiling new features, such as the continuous evolution of their propagation direction with frequency, tilted wavefronts and asymmetric responses. The interplay between diagonal loss and off-diagonal shear phenomena in the dielectric response of these materials has implications for new forms of non-Hermitian and topological photonic states. We anticipate that our results will motivate new directions for polariton physics in low-symmetry materials, which include geological minerals, many common oxides and organic crystals, greatly expanding the material base and extending design opportunities for compact photonic devices
Optical variability properties of high luminosity AGN classes
We present the results of a comparative study of the intra-night optical
variability (INOV) characteristics of radio-loud and radio-quiet quasars, which
involves a systematic intra-night optical monitoring of seven sets of high
luminosity AGNs covering the redshift range {\it z} to {\it z}
. The sample, matched in the optical luminosity -- redshift (M
-- z) plane, consists of seven radio-quiet quasars (RQQs), eight radio
lobe-dominated quasars (LDQs), six radio core-dominated quasars (CDQs) and five
BL Lac objects (BLs). Systematic CCD observations, aided by a careful data
analysis procedure, have allowed us to detect INOV with amplitudes as low as
1%. Present observations cover a total of 113 nights (720 hours) with only a
single quasar monitored as continuously as possible on a night. Considering
cases of only unambiguous detections of INOV we have estimated duty cycles
(DCs) of 17%, 12%, 20% and 72% respectively for RQQs, LDQs, CDQs, and BLs. The
low amplitude and low DC of INOV shown by RQQs compared to BLs can be
understood in terms of their having optical synchrotron jets which are modestly
misdirected from us. From our fairly extensive dataset, no unambiguous general
trend of a correlation between the INOV amplitude and the apparent optical
brightness of the quasar is noticed.Comment: 36 pages, 14 Figures, due to large size Fig. 5,6,11 and 12 are not
included. Intersted people contact to [email protected]. Submitted to
Journal of Astrophysics and Astronom
Day-Scale Variability of 3C 279 and Searches for Correlations in Gamma-Ray, X-Ray, and Optical Bands
Light curves of 3C 279 are presented in optical (R-band), X-rays (RXTE/PCA),
and gamma rays (CGRO/EGRET) for 1999 Jan-Feb and 2000 Jan-Mar. During both of
those epochs the gamma-ray levels were high, and all three observed bands
demonstrated substantial variation, on time scales as short as one day.
Correlation analyses provided no consistent pattern, although a rather
significant optical/gamma-ray correlation was seen in 1999, with a gamma-ray
lag of ~2.5 days, and there are other suggestions of correlations in the light
curves. For comparison, correlation analysis is also presented for the
gamma-ray and X-ray light curves during the large gamma ray flare in 1996 Feb
and the two gamma-bright weeks leading up to it; the correlation at that time
was strong, with a gamma-ray/X-ray offset of no more than 1 day.Comment: 20 pages, including 7 figures; accepted by The Astrophysical Journa
INFLAMMATORY BOWEL DISEASE AND COLORECTAL CANCER, NUTRACEUTICAL ASPECTS
Nutraceuticals constitute a group of functional foods that provide added health benefits for various disorders including inflammatory bowel disease (IBD) and colorectal cancer (CCR). The main groups of nutraceuticals include probiotics, prebiotics omega 3 and antioxidants. Studies on nutraceutical showed that this type of food possessed similar properties to drugs but with the benefit of not having side effects. This mini review shows that probiotics and prebiotics, when administered simultaneously with traditional therapies, reduce IBD symptoms and reduce synthesis of enzymes probably involved in colorectal carcinogenesis. Moreover, Omega 3 reduces the synthesis of inflammation mediators and prevenents carcinogenesis through interaction interaction with the signaling pathway NOTCH1/MMP9. Moreover, antioxidant reduce the inflammatory process by inhibiting the synthesis of inflammatory mediators, and inhibit the mechanisms of cell proliferation by inducing apoptosis. In brief, nutraceuticals have gained a huge clinical interest since they could be used along with traditional therapy. Bioavailability studies of nutracetical supplements guarantee a correct intake of the substance by oral administration, a matter which would not have been posible to have entirely with the consumprtion of regular food only
Rms-flux relation in the optical fast variability data of BL Lacertae object S5 0716+714
The possibility that BL Lac S5 0716+714 exhibits a linear root mean square
(rms)-flux relation in its IntraDay Variability (IDV) is analysed. The results
may be used as an argument in the existing debate regarding the source of
optical IDV in Active Galactic Nuclei. 63 time series in different optical
bands were used. A linear rms-flux relation at a confidence level higher than
65% was recovered for less than 8% of the cases. We were able to check if the
magnitude is log-normally distributed for eight timeseries and found, with a
confidence > 95%, that this is not the case.Comment: Accepted by Astrophysics and Space Scienc
Internet self-efficacy does not predict student use of Internet-mediated educational technology
Two studies tested the hypothesis that use of learning technologies among undergraduate psychology students was associated with higher Internet self-efficacy (ISE). In Study 1, the ISE scores of 86 students were found not to be associated with either attitudes towards, or measured use of, blogs and wikis as part of an IT skills course. ISE was associated with time spent online, and positive attitudes to wikis were associated with higher use. Study 2 measured 163 students’ ISE scores at the beginning and end of the same course. ISE was again not correlated with attitudes towards, or actual measured use of, learning technologies used in the course. However, ISE was shown to increase during the course. Positive attitudes towards wikis and discussion boards were associated with higher use of each. Overall, ISE scores did not influence measured use of a Virtual Learning Environment (VLE, including blogs, wikis and a discussion board), or attitudes towards those technologies. This implies that while ISE is linked to aspects of online behaviour (time spent online) and can be modified by online activity or training, it does not predict student use of educational Internet technologies
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