19,821 research outputs found
Quantum ratchet transport with minimal dispersion rate
We analyze the performance of quantum ratchets by considering the dynamics of
an initially localized wave packet loaded into a flashing periodic potential.
The directed center-of-mass motion can be initiated by the uniform modulation
of the potential height, provided that the modulation protocol breaks all
relevant time- and spatial reflection symmetries. A poor performance of quantum
ratchet transport is characterized by a slow net motion and a fast diffusive
spreading of the wave packet, while the desirable optimal performance is the
contrary. By invoking a quantum analog of the classical P\'eclet number, namely
the quotient of the group velocity and the dispersion of the propagating wave
packet, we calibrate the transport properties of flashing quantum ratchets and
discuss the mechanisms that yield low-dispersive directed transport.Comment: 6 pages; 3 figures; 1 tabl
Cold atom realizations of Brownian motors
Brownian motors are devices which "rectify" Brownian motion, i.e. they can
generate a current of particles out of unbiased fluctuations. Brownian motors
are important for the understanding of molecular motors, and are also promising
for the realization of new nanolelectronic devices. Among the different systems
that can be used to study Brownian motors, cold atoms in optical lattices are
quite an unusual one: there is no thermal bath and both the potential and the
fluctuations are determined by laser fields. In this article recent
experimental implementations of Brownian motors using cold atoms in optical
lattices are reviewed
Three dimensional asset documentation using terrestrial laser scanner technology
Asset documentation is a detailed record or inventory of the properties located within a room or a building. It is important to record the assets in case of property loss happen inside the premise especially when that premise caught fire, earthquake, robbery and others. The instrument used in this study is Faro Laser Scanner Photon 120/20. The object of the study is the computer room of Photogrammetry Lab, Faculty of Geoinformation and Real Estate. The final output of this study is the 3D model of the assets available inside the building. Before 3D model can be formed, the scanned data which is in the form of point cloud generated from the laser scanner have to be registered and georeferenced in order to combine the scans. The combine scans is the representation of the whole area of work surveyed from every scan points. These processes use Faro Scene, software that comes together with the laser scanner. By introducing this method, large scale asset documentation such as for factories and schools would be very beneficial rather than conventional method. The next process is to model the point cloud using AutoCAD 2011. Every item available on the room such as desks, chairs, cubicles, computers, whiteboard, projectors and cupboard are modeled and each of these items was inserted with attributes so that we can know the information of each item
The flashing behavior of thunderstorms
Lightning flash distribution in thunderstorms - statistical analysi
On outer fluctuations for internal DLA
We had established inner and outer fluctuation for the internal DLA cluster
when all walks are launched from the origin. In obtaining the outer
fluctuation, we had used a deep lemma of Jerison, Levine and Sheffield, which
estimate roughly the possibility of fingering, and had provided a simple proof
using an interesting estimate for crossing probability for a simple random
walk. The application of the crossing probability to the fingering for the
internal DLA cluster contains a flaw discovered recently, that we correct in
this note. We take the opportunity to make a self-contained exposition.Comment: 10 page
A TROPOMI- and GLM-Based Estimate of NOx Production by Lightning over the U.S.
Lightning produces NO because the extreme temperatures (>20000 K) in lightning channels dissociate molecular O2 and molecular N2, which then combine to form NOx which quickly reacts with O3 to form NO2. Lightning is responsible for 10-15% of NOx emissions globally. This is 2 8 Tg N a-1 [Schumann and Huntrieser, 2007] or 100 to 400 mol per flash. Much of the uncertainty stems from limited knowledge of lightning NOx production per flash (LNOx PE) or per unit flash length. Most LNOx is injected into mid- and upper-troposphere where away from deep convection its lifetime is longer relative to lower troposphere NOx. NOx in this region enhances the concentrations of upper tropospheric NOy, OH, and O3 and contributes to positive radiative forcing by O3 and negative forcing by CH4. We have previously used OMI NO2 to obtain estimates of LNOx production per flash over the Gulf of Mexico (Pickering et al., 2016, JGR), in convective events during NASAs TC4 field program (Bucsela et al., 2010, JGR), and over broad regions of the tropics (Allen et al., 2019, JGR) and midlatitudes (Bucsela et al., 2019, JGR). In the latter studies, we obtained PE values of 170 100 mol flash and 180 100 mol flash, respectively
The structure of lightning flashes HF-UHF: 12 September 1975, Atlanta, Georgia
Simultaneous measurement of sferics at 3, 30, 139, and 295 MHz were made during thunderstorms. Wideband electronics and an analogue tape recorder continuously recorded the radiation from lightning with about 300 kHz of bandwidth. The data were obtained during the passage of a cold front. Flashing rate, burst rate and the structure of individual flashes were recorded. The record of a typical flash begins with a sudden burst of closely spaced pulses whose temporal structure is typical of the stepped leader, and ends in a large pulse suggestive of a first return stroke. The remainder of the flash consists of a sequence of pulses of varying amplitude separated by quiet periods of the order of milliseconds. The shape of these pulses and the temporal structure suggest that the first few large pulses are return strokes. Other discharges begin with widely spaced discrete pulses and resemble the preceding discharge less the leader and return stroke phase. The radiation exhibits a similar structure, at each of the frequencies monitored
Directed transport of Brownian particles in a double symmetric potential
We investigate the dynamics of Brownian particles in internal state-
dependent symmetric and periodic potentials. Although no space or time symmetry
of the Hamiltonian is broken, we show that directed transport can appear. We
demonstrate that the directed motion is induced by breaking the symmetry of the
transition rates between the potentials when these are spatially shifted.
Finally, we discuss the possibility of realizing our model in a system of cold
particles trapped in optical lattices.Comment: to appear in Physical Review
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