1,441 research outputs found
Quantum Coherence Effects in Four-level Diamond Atomic System
A symmetric four-level closed-loop type (the diamond
structure) atomic system driven by four coherent optical fields is
investigated. The system shows rich quantum interference and coherence
features. When symmetry of the system is broken, interesting phenomena such as
single and double dark resonances appear. As a result, the double
electromagnetically induced transparency effect is generated, which will
facilitate the implementation of quantum phase gate operation.Comment: 8pages, 19 figure
Increased Sensitivity to Possible Muonium to Antimuonium Conversion
A new experimental search for muonium-antimuonium conversion was conducted at
the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis
yielded one event fulfilling all required criteria at an expected background of
1.7(2) events due to accidental coincidences. An upper limit for the conversion
probability in 0.1 T magnetic field is extracted as (90%
CL).Comment: 2 figure
A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging
We provide a quantitative description and statistical interpretation of the
optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS)
has obtained repeated imaging in five UV-to-IR photometric bands for 33,881
spectroscopically confirmed quasars. About 10,000 quasars have an average of 60
observations in each band obtained over a decade along Stripe 82 (S82), whereas
the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed
time lags span the range from a day to almost 10 years, and constrain quasar
variability at rest-frame time lags of up to 4 years, and at rest-frame
wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of
quasars from the SDSS Data Release 7 that have been observed at least twice in
SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it
to analyze the ensemble properties of quasar variability. Based on a damped
random walk (DRW) model defined by a characteristic time scale and an
asymptotic variability amplitude that scale with the luminosity, black hole
mass, and rest wavelength for individual quasars calibrated in S82, we can
fully explain the ensemble variability statistics of the non-S82 quasars such
as the exponential distribution of large magnitude changes. All available data
are consistent with the DRW model as a viable description of the optical
continuum variability of quasars on time scales of ~5-2000 days in the rest
frame. We use these models to predict the incidence of quasar contamination in
transient surveys such as those from PTF and LSST.Comment: 33 pages, 19 figures, replaced with accepted version. Catalog is
available at http://www.astro.washington.edu/users/ivezic/macleod/qso_dr7
Hydrogen and Metal Line Absorption Around Low-Redshift Galaxies in Cosmological Hydrodynamic Simulations
We study the physical conditions of the circum-galactic medium (CGM) around
z=0.25 galaxies as traced by HI and metal line absorption, using cosmological
hydrodynamic simulations that include galactic outflows. Using lines of sight
targeted at impact parameters from 10 kpc to 1 Mpc around galaxies with halo
masses from 10^11-10^13 M_solar, we study the physical conditions and their
variation with impact parameter b and line-of-sight velocity delta v in the CGM
as traced by HI, MgII, SiIV, CIV, OVI, and NeVIII absorbers. All ions show a
strong excess of absorption near galaxies compared to random lines of sight.
The excess continues beyond 1 Mpc, reflecting the correlation of metal
absorption with large-scale structure. Absorption is particularly enhanced
within about v<300 km/sec and roughly 300 kpc of galaxies (with distances
somewhat larger for the highest ion), approximately delineating the CGM; this
range contains the majority of global metal absorption. Low ions like MgII and
SiIV predominantly arise in denser gas closer to galaxies and drop more rapidly
with b, while high ions OVI and NeVIII trace more diffusely distributed gas
with a comparatively flat radial profile; CIV is intermediate. All ions
predominantly trace T~10^4-4.5 K photo-ionised gas at all b, but when hot CGM
gas is present (mostly in larger halos), we see strong collisionally-ionised
OVI and NeVIII at b <= 100 kpc. Larger halo masses generally produce more
absorption, though overall the trends are not as strong as that with impact
parameter. These findings arise using our favoured outflow scalings as expected
for momentum-driven winds; with no winds, the CGM gas remains mostly
unenriched, while our outflow model with a constant velocity and mass loading
factor produce hotter, more widely dispersed metals.Comment: 26 pages, 15 figures, published in MNRAS. Updates to citations from
previous versio
Alterations and test-retest reliability of functional connectivity network measures in cerebral small vessel disease
While structural network analysis consolidated the hypothesis of cerebral small vessel disease (SVD) being a disconnection syndrome, little is known about functional changes on the level of brain networks. In patients with genetically defined SVD (CADASIL,n= 41) and sporadic SVD (n= 46), we independently tested the hypothesis that functional networks change with SVD burden and mediate the effect of disease burden on cognitive performance, in particular slowing of processing speed. We further determined test-retest reliability of functional network measures in sporadic SVD patients participating in a high-frequency (monthly) serial imaging study (RUN DMC-InTENse, median: 8 MRIs per participant). Functional networks for the whole brain and major subsystems (i.e., default mode network, DMN;fronto-parietal task control network, FPCN;visual network, VN;hand somatosensory-motor network, HSMN) were constructed based on resting-state multi-band functional MRI. In CADASIL, global efficiency (a graph metric capturing network integration) of the DMN was lower in patients with high disease burden (standardized beta = -.44;p[corrected] = .035) and mediated the negative effect of disease burden on processing speed (indirect path: std. beta = -.20,p= .047;direct path: std. beta = -.19,p= .25;total effect: std. beta = -.39,p= .02). The corresponding analyses in sporadic SVD showed no effect. Intraclass correlations in the high-frequency serial MRI dataset of the sporadic SVD patients revealed poor test-retest reliability and analysis of individual variability suggested an influence of age, but not disease burden, on global efficiency. In conclusion, our results suggest that changes in functional connectivity networks mediate the effect of SVD-related brain damage on cognitive deficits. However, limited reliability of functional network measures, possibly due to age-related comorbidities, impedes the analysis in elderly SVD patients
Quantum superposition of localized and delocalized phases of photons
Based on a variant of 2-site Jaynes-Cummings-Hubbard model, which is
constructed using superconducting circuits, we propose a method to coherently
superpose the localized and delocalized phases of photons. In our model, two
nonlinear superconducting stripline resonators are coupled by an interfacial
circuit composed of parallel combination of a superconducting qubit and a
capacitor, which plays the role of a quantum knob for the photon hopping rate:
with the knob qubit in its ground/excited state, the injected photons tend to
be localized/delocalized in the resonators. We show that, by applying a
microwave field with appropriate frequency on the knob qubit, we could
demonstrate Rabi oscillation between photonic localized phase and delocalized
phase. Furthermore, this set-up offers advantages (e. g. infinite on/off ratio)
over other proposals for the realization of scalable quantum computation with
superconducting qubits.Comment: 4 pages, 4 figure
Rituals Improve Children's Ability to Delay Gratification
To be accepted into social groups, individuals must internalize and reproduce appropriate group conventions, such as rituals. The copying of such rigid and socially stipulated behavioral sequences places heavy demands on executive function. Given previous research showing that challenging executive functioning improves it, it was hypothesized that engagement in ritualistic behaviors improves children's executive functioning, in turn improving their ability to delay gratification. A 3-month circle time games intervention with 210 schoolchildren (Mage = 7.78 years, SD = 1.47) in two contrasting cultural environments (Slovakia and Vanuatu) was conducted. The intervention improved children's executive function and in turn their ability to delay gratification. Moreover, these effects were amplified when the intervention task was imbued with ritual, rather than instrumental, cues
Surface modification of Ti-4Al-2V alloy by nitrogen implantation
Ti-4Al-2V is a new type of alpha titanium alloy that suitable for the application in high-temperature and high-pressure water/steam environment. Ti-4Al-2V can be used in marine engineering, nuclear power industry. In this paper the surface characterization of the Ti-4Al-2V implanted with 75 keV nitrogen with fluences of 3 × 10 17 and 8 × 10 17 N + /cm 2 is investigated by glancing-incidence XRD, XPS and microhardness. The results show that new phase TiN are formed after N implantation in the surface region. The nitrogen implantation increases the surface hardness up to 340 and 260% for fluence of 8 × 10 17 and 3 × 10 17 N + /cm 2 , respectively. The enhancement of hardness is related to the formation of TiN and irradiation induced hardness.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43177/1/10853_2005_Article_5365.pd
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