298 research outputs found
Energy landscape of resting magnetoencephalography reveals frontoparietal network impairments in epilepsy
Juvenile myoclonic epilepsy (JME) is a form of idiopathic generalized epilepsy. It is yet unclear to what extent JME leads to abnormal network activation patterns. Here, we characterised statistical regularities in MEG resting-state networks and their differences between JME patients and controls, by combining a pairwise maximum entropy model (pMEM) and novel energy landscape analyses for MEG. First, we fitted the pMEM to the MEG oscillatory power in the frontoparietal network (FPN) and other resting-state networks, which provided a good estimation of the occurrence probability of network states. Then, we used energy values derived from the pMEM to depict an energy landscape, with a higher energy state corresponding to a lower occurrence probability. JME patients showed fewer local energy minima than controls and had elevated energy values for the FPN within the theta, beta and gamma-bands. Furthermore, simulations of the fitted pMEM showed that the proportion of time the FPN was occupied within the basins of energy minima was shortened in JME patients. These network alterations were highlighted by significant classification of individual participants employing energy values as multivariate features. Our findings suggested that JME patients had altered multi-stability in selective functional networks and frequency bands in the frontoparietal cortices
CCD Photometry of Faint Variable Stars in the Globular Cluster NGC 6752
We present the results of a photometric survey for variable stars in the
field of the nearby globular cluster NGC 6752. The cluster was monitored in
1996 and 1997 for a total of 54 hours with 3 different CCD cameras mounted on
the 1.0-m Swope telescope. Eleven new variables were identified: 3 SX Phe
stars, 7 contact binaries and 1 candidate detached eclipsing binary. All 3 SX
Phe variables are likely members of the cluster while only 1 out of the 7
contact binaries is a potential cluster member. As a by-product of our survey
we obtained UBV photometry for a large sample of stars in the cluster field.
Two stars with U-B \approx -1.0 and V=19.3 and V=20.6 were identified. They lie
along the extended horizontal branch of the cluster, and are likely to be faint
sdB stars from NGC 6752.Comment: 18 pages, LaTex, 9 figures (Fig. 1 not available), accepted for
publication in the Astronomical Journa
Concentrating Membrane Proteins Using Asymmetric Traps and AC Electric Fields
Membrane proteins are key components of the plasma membrane and are responsible for control of chemical ionic gradients, metabolite and nutrient transfer, and signal transduction between the interior of cells and the external environment. Of the genes in the human genome, 30% code for membrane proteins (Krogh et al. J. Mol. Biol.2001, 305, 567). Furthermore, many FDA-approved drugs target such proteins (Overington et al. Nat. Rev. Drug Discovery2006, 5, 993). However, the structure-function relationships of these are notably sparse because of difficulties in their purification and handling outside of their membranous environment. Methods that permit the manipulation of membrane components while they are still in the membrane would find widespread application in separation, purification, and eventual structure-function determination of these species (Poo et al. Nature1977, 265, 602). Here we show that asymmetrically patterned supported lipid bilayers in combination with AC electric fields can lead to efficient manipulation of charged components. We demonstrate the concentration and trapping of such components through the use of a “nested trap” and show that this method is capable of yielding an approximately 30-fold increase in the average protein concentration. Upon removal of the field, the material remains trapped for several hours as a result of topographically restricted diffusion. Our results indicate that this method can be used for concentrating and trapping charged membrane components while they are still within their membranous environment. We anticipate that our approach could find widespread application in the manipulation and study of membrane proteins
Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4
We report the detection of pulsations with s period in V2116 Oph,
the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are
sinusoidal with modulation amplitude of up to 4% in blue light and were
observed in ten different observing sessions during 1996 April-August using a
CCD photometer at the 1.6-m and 0.6-m telescopes of Laborat\'orio Nacional de
Astrof\'{\i}sica, in Brazil. The pulsations were also observed with the
fast photometer. With only one exception the observed optical periods are
consistent with those observed by the BATSE instrument on board the Compton
Gamma Ray Observatory at the same epoch. There is a definite correlation
between the observability of pulsations and the optical brightness of the
system: V2116~Oph had magnitude in the range when the pulsed
signal was detected, and when no pulsations were present. The
discovery makes GX 1+4 only the third of accretion-powered X-ray
pulsars to be firmly detected as a pulsating source in the optical. The
presence of flickering and pulsations in V2116 Oph adds strong evidence for an
accretion disk scenario in this system. The absolute magnitude of the pulsed
component on 1996 May 27 is estimated to be . The implied
dimensions for the emitting region are 1.1 R_{\sun}, 3.2 R_{\sun}, and 7.0
R_{\sun}, for black-body spectral distributions with K, K, and K, respectively.Comment: 9 pages, 3 figures in PostScript, latex, accepted for publication on
the Astrophysical Journal Letter
Observations of Faint Eclipsing Cataclysmic Variables
We present time-resolved photometry of six faint (V>17mag) cataclysmic
variables (CVs); one of them is V849 Oph and the others are identified from the
Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139,
SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations
of these objects were performed at the T\"UB\.ITAK National Observatory
(Turkey) between February 2006 and March 2009. We aimed to detect short time
scale orbital variability arisen from hot-spot modulation, flickering
structures which occur from rapid fluctuations of material transferring from
red star to white dwarf and orbital period changes for selected short-period
(P<4h) CVs at quiescence. Results obtained from eclipse timings and light
curves morphology related to white dwarf stars, accretion disks and hot-spots
are discussed for each system. Analysis of the short time coverage of data,
obtained for SDSS J1227+5139 indicates a cyclical period change arisen from
magnetic activity on the secondary star. Photometric period of SDSS J1607+3623
is derived firstly in this study, while for the other five systems light
elements are corrected using the previous and new photometric observations. The
nature of SDSS J1457+5148 is not precisely revealed that its light curve shows
any periodicity that could be related to the orbital period
A New Photomechanical Molecular Switch Based on a Linear {\pi}-Conjugated System
We report the electronic transport properties of a new photo-addressable
molecular switch. The switching process relies on a new concept based on linear
{\pi}-conjugated dynamic systems, in which the geometry and hence the
electronic properties of an oligothiophene chain can be reversibly modified by
the photochemical trans-cis isomerization of an azobenzene unit fixed in a
lateral loop. Electron transport measurements through self-assembled monolayers
on gold, contacted with eGaIn top contact, show switching with a conductance
ratio up to 1E3. Ab initio calculations have been used to identify the most
energetically stable conformations of the molecular switch, the corresponding
calculated conductances qualitatively explain the trend observed in the
photo-switching experiments.Comment: Full manuscript and supporting information, J. Phys. Chem.
C,published on line (2017
A New Photomechanical Molecular Switch Based on a Linear {\pi}-Conjugated System
We report the electronic transport properties of a new photo-addressable
molecular switch. The switching process relies on a new concept based on linear
{\pi}-conjugated dynamic systems, in which the geometry and hence the
electronic properties of an oligothiophene chain can be reversibly modified by
the photochemical trans-cis isomerization of an azobenzene unit fixed in a
lateral loop. Electron transport measurements through self-assembled monolayers
on gold, contacted with eGaIn top contact, show switching with a conductance
ratio up to 1E3. Ab initio calculations have been used to identify the most
energetically stable conformations of the molecular switch, the corresponding
calculated conductances qualitatively explain the trend observed in the
photo-switching experiments.Comment: Full manuscript and supporting information, J. Phys. Chem.
C,published on line (2017
No apparent accretion mode changes detected in Cen X-3
The presence of two distinct spectral states has previously been reported for
Cen X-3 on the basis of RXTE/ASM observations. Triggered by this result, we
investigated the spectral properties of the source using the larger amount of
X-ray data now available with the aim to clarify and interpret the reported
behavior. To check the reported results we used the same data set and followed
the same analysis procedures as in the work reporting the two spectral states.
Additionally, we repeated the analysis using the enlarged data sample including
the newest RXTE/ASM observations as well as the data from the MAXI monitor and
from the INTEGRAL/JEM-X and ISGRI instruments. We could not confirm the
reported presence of the two spectral states in Cen X-3 either inComment: 4 pages, 6 figures, article is accepted for Astronomy & Astrophysic
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