9,029 research outputs found
Equivalence of glass transition and colloidal glass transition in the hard-sphere limit
We show that the slowing of the dynamics in simulations of several model
glass-forming liquids is equivalent to the hard-sphere glass transition in the
low-pressure limit. In this limit, we find universal behavior of the relaxation
time by collapsing molecular-dynamics data for all systems studied onto a
single curve as a function of , the ratio of the temperature to the
pressure. At higher pressures, there are deviations from this universal
behavior that depend on the inter-particle potential, implying that additional
physical processes must enter into the dynamics of glass-formation.Comment: 4 pages, 4 figure
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Enhanced Raman Detection System based on a Hollow-core Fiber Probe design
This paper focus on an enhanced Raman-based detection probe and its performance evaluated. The probe employs a hollow-core fiber design to allow liquid micro-sample to be analyzed. The hollow-core fiber is used both to transmit the light signal used to excite the sample and to collect the Raman scattering signal received from the micro-sample under analysis. In order to maximize the performance of the system, various parameters have been studied experimentally, including the diameter and the height of the liquid sample in the probe. The aim has been optimizing both as a means to enhance the Raman scattering signal received from the liquid sample. As a result, a Raman-based detection probe using a reflector approach was developed and evaluated. This design enabling a greater area for interaction with the sample to be formed and to concentrate the excitation light into it. This then increases the efficiency of the light-liquid interaction and improves the collection efficiently of the forward Raman scattering light signal. With the use of this design, the detected Raman scattering signal was increased by a factor of 103~104 over what otherwise would be achieved. A key feature is that with the use of a hollow-core fiber to collect the liquid sample, only a very small volume is needed, making this well suited to practical applications where limited amounts of material are available e.g. biofluids or high value liquids. The system designed and evaluated thus provides the basis of an effective all-fiber Raman-based detection system, capable of being incorporated into portable analysis equipment for rapid detection and in-the-field use
Electrical Transport in High Quality Graphene pnp Junctions
We fabricate and investigate high quality graphene devices with contactless,
suspended top gates, and demonstrate formation of graphene pnp junctions with
tunable polarity and doping levels. The device resistance displays distinct
oscillations in the npn regime, arising from the Fabry-Perot interference of
holes between the two pn interfaces. At high magnetic fields, we observe
well-defined quantum Hall plateaus, which can be satisfactorily fit to
theoretical calculations based on the aspect ratio of the device.Comment: to appear in a special focus issue in New Journal of Physic
^{59}Co NMR evidence for charge ordering below T_{CO}\sim 51 K in Na_{0.5}CoO_2
The CoO layers in sodium-cobaltates NaCoO may be viewed as
a spin triangular-lattice doped with charge carriers. The underlying
physics of the cobaltates is very similar to that of the high cuprates.
We will present unequivocal Co NMR evidence that below ,
the insulating ground state of the itinerant antiferromagnet
NaCoO () is induced by charge ordering.Comment: Phys. Rev. Lett. 100 (2008), in press. 4 figure
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High Sensitivity Hot-wire based Wind Velocity Sensor using Co-doped Fiber and Fiber Bragg Grating for use in mining applications
In this paper, a mathematical model of the temperature distribution in a fiber-optic version of the familiar 'hot-wire' wind velocity sensor has been established and a practical sensor device realized and investigated for use in coal mining applications. The relationship between the dynamic measurement range, the sensitivity, the sensor probe surface heat transfer coefficient and the wind speed (in the region where the sensor probe is located) has been investigated. The veracity of the predicted performance of the fiber-optic hot-wire mathematical model has then been verified by experiment. The sensitivity of the sensor probe to wind velocity was measured across several wind velocity ranges to be ∼1500pm per unit m/s wind velocity (in the range of 0 - 0.5 m/s), ∼330pm per unit m/s in the range 0.5 - 2 m/s and ∼50pm per unit m/s in the range of 2.0 - 4.5 m/s
Rapid "Turn-on" of type 1 AGN in a quiescent early type galaxy SDSS1115+0544
We present a detailed study of a transient in the center of SDSS1115+0544
based on the extensive UV, optical, mid-IR light curves (LC) and spectra over
1200 days. The host galaxy is a quiescent early type galaxy at = 0.0899
with a blackhole mass of . The transient underwent a 2.5
magnitude brightening over days, reaching a peak -band luminosity
(extinction corrected) of magnitude, then fading 0.5 magnitude over 200
days, settling into a plateau of days. Following the optical brightening
are the significant mid-IR flares at and m, with a peak time
delay of days. The mid-IR LCs are explained as the echo of UV photons
by a dust medium with a radius of cm, consistent with of 0.58 inferred from the spectra. This event is very energetic with an
extinction corrected erg s. Optical
spectra over 400 days in the plateau phase revealed newly formed broad
H emission with a FWHM of km s and narrow
coronal lines such as [Fe VII], [Ne V]. This flare also has a steeply rising UV
continuum, detected by multi-epoch data at to days post
optical peak. The broad Balmer lines and the UV continuum do not show
significant temporal variations. The slow evolving LCs over 1200 days, the
constant Balmer lines and UV continuum at late-times rule out TDE and SN IIn as
the physical model for this event. We propose that this event is a `turn-on'
AGN, transitioning from a quiescent state to a type 1 AGN with a sub-Eddington
accretion rate of /yr. This change occurred on a very short time
scale of days. The discovery of such a rapid `turn-on' AGN
poses challenges to accretion disk theories and may indicate such event is not
extremely rare.Comment: Comments are welcome. Emails to the first author. Accepted for
publication in Ap
Origin of the Weak Pseudo-gap Behaviors in Na_{0.35}CoO_2: Absence of Small Hole Pockets
We analyze the ``normal electronic states'' of Na_{0.35}CoO_2 based on the
effective d-p model with full d-orbital freedom using the fluctuation-exchange
(FLEX) approximation. They sensitively depend on the topology of the Fermi
surfaces, which changes as the crystalline electric splitting (CES) due to the
trigonal deformation. We succeed in reproducing the weak pseudo-gap behaviors
in the density of states (DOS) and in the uniform magnetic susceptibility below
300K, assuming that six small hole-pockets predicted by LDA band calculations
are absent. When they exist, on the contrary, then ``anti-pseudo-gap
behaviors'' should inevitably appear. Thus, the present study strongly supports
the absence of the small hole-pockets in Na_{0.35}CoO_2, as reported by recent
ARPES measurements. A large Fermi surface around the \Gamma-point would account
for the superconductivity in water-intercalated samples.Comment: 5pages, to appear in J. Phys. Soc. Jpn. Vol.74 (2005) No.
Momentum Distribution for Bosons with Positive Scattering Length in a Trap
The coordinate-momentum double distribution function is calculated in the local density approximation for bosons with
positive scattering length in a trap. The calculation is valid to the first
order of . To clarify the meaning of the result, it is compared for a
special case with the double distribution function of
Wigner.Comment: Latex fil
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