273 research outputs found
Small scale unit for groundwater treatment
Small scale unit for groundwater treatmen
Mapping the ultrafast flow of harvested solar energy in living photosynthetic cells
Photosynthesis transfers energy efficiently through a series of antenna complexes to the
reaction center where charge separation occurs. Energy transfer in vivo is primarily monitored
by measuring fluorescence signals from the small fraction of excitations that fail to
result in charge separation. Here, we use two-dimensional electronic spectroscopy to follow
the entire energy transfer process in a thriving culture of the purple bacteria, Rhodobacter
sphaeroides. By removing contributions from scattered light, we extract the dynamics of
energy transfer through the dense network of antenna complexes and into the reaction
center. Simulations demonstrate that these dynamics constrain the membrane organization
into small pools of core antenna complexes that rapidly trap energy absorbed by surrounding
peripheral antenna complexes. The rapid trapping and limited back transfer of these excitations
lead to transfer efficiencies of 83% and a small functional light-harvesting unit
AURA - A radio frequency extension to IceCube
The excellent radio frequency transparency of cold polar ice, combined with
the coherent Cherenkov emission produced by neutrino-induced showers when
viewed at wavelengths longer than a few centimeters, has spurred considerable
interest in a large-scale radio-wave neutrino detector array.
The AURA (Askaryan Under-ice Radio Array) experimental effort, within the
IceCube collaboration, seeks to take advantage of the opportunity presented by
IceCube drilling through 2010 to establish the radio frequency technology
needed to achieve 100-1000 km^3 effective volumes.
In the 2006-2007 Austral summer 3 deep in-ice radio frequency (RF) clusters
were deployed at depths of 1300m and 300m on top of the IceCube strings.
Additional 3 clusters will be deployed in the Austral summer of 2008-2009.
Verification and calibration results from the current deployed clusters are
presented, and the detector design and performances are discussed. Augmentation
of IceCube with large-scale 1000km^3sr radio and acoustic arrays would extend
the physics reach of IceCube into the EeV-ZeV regime and offer substantial
technological redundancy.Comment: To appear in the proceedings of the Acoustic and Radio EeV Neutrino
detection Activities (ARENA) 2008 conferenc
Quantum computation and the physical computation level of biological information processing
On the basis of introspective analysis, we establish a crucial requirement
for the physical computation basis of consciousness: it should allow processing
a significant amount of information together at the same time. Classical
computation does not satisfy the requirement. At the fundamental physical
level, it is a network of two body interactions, each the input-output
transformation of a universal Boolean gate. Thus, it cannot process together at
the same time more than the three bit input of this gate - many such gates in
parallel do not count since the information is not processed together. Quantum
computation satisfies the requirement. At the light of our recent explanation
of the speed up, quantum measurement of the solution of the problem is
analogous to a many body interaction between the parts of a perfect classical
machine, whose mechanical constraints represent the problem to be solved. The
many body interaction satisfies all the constraints together at the same time,
producing the solution in one shot. This shades light on the physical
computation level of the theories that place consciousness in quantum
measurement and explains how informations coming from disparate sensorial
channels come together in the unity of subjective experience. The fact that the
fundamental mechanism of consciousness is the same of the quantum speed up,
gives quantum consciousness a potentially enormous evolutionary advantage.Comment: 13 page
Planar lattice gases with nearest-neighbour exclusion
We discuss the hard-hexagon and hard-square problems, as well as the
corresponding problem on the honeycomb lattice. The case when the activity is
unity is of interest to combinatorialists, being the problem of counting binary
matrices with no two adjacent 1's. For this case we use the powerful corner
transfer matrix method to numerically evaluate the partition function per site,
density and some near-neighbour correlations to high accuracy. In particular
for the square lattice we obtain the partition function per site to 43 decimal
places.Comment: 16 pages, 2 built-in Latex figures, 4 table
Prenatal phthalate exposure and performance on the Neonatal Behavioral Assessment Scale in a multiethnic birth cohort
We investigated the relationship between prenatal maternal urinary concentrations of phthalate metabolites and neonatal behavior in their 295 children enrolled in a multiethnic birth cohort between 1998 and 2002 at the Mount Sinai School of Medicine in New York City. Trained examiners administered the Brazelton Neonatal Behavioral Assessment Scale (BNBAS) to children within 5 days of delivery. We measured metabolites of 7 phthalate esters in maternal urine that was collected between 25 and 40 weeks' gestation. All but two phthalate metabolites were over 95% detectable. We summed metabolites on a molar basis into low and high molecular weight phthalates. We hypothesized the existence of sex-specific effects from phthalate exposure a priori given the hormonal activity of these chemicals. Overall we found few associations between individual phthalate metabolites or their molar sums and most of the BNBAS domains. However, we observed significant sex-phthalate metabolite interactions (p < 0.10) for the Orientation and Motor domains and the overall Quality of Alertness score. Among girls, there was a significant linear decline in adjusted mean Orientation score with increasing urinary concentrations of high molecular weight phthalate metabolites (B = -0.37, p = 0.02). Likewise, there was a strong linear decline in their adjusted mean Quality of Alertness score (B = -0.48, p < 0.01). In addition, boys and girls demonstrated opposite patterns of association between low and high molecular weight phthalate metabolite concentrations and motor performance, with some indication of improved motor performance with increasing concentration of low molecular weight phthalate metabolites among boys. This is the first study to report an association between prenatal phthalate exposure and neurological effects in humans or animals, and as such requires replication
Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass
Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T
pulsed magnetic fields. The CF effective mass is found to increase
approximately linearly with the effective field , in agreement with our
earlier work at lower fields. For a of 14 T it reaches , over 20
times the band edge electron mass. Data from all fractions are unified by the
single parameter for all the samples studied over a wide range of
electron densities. The energy gap is found to increase like at
high fields.Comment: Has final table, will LaTeX without error
Communication: Broad manifold of excitonic states in light-harvesting complex 1 promotes efficient unidirectional energy transfer in vivo
In photosynthetic organisms, the pigment-protein complexes that comprise the light-harvesting
antenna exhibit complex electronic structures and ultrafast dynamics due to the coupling among
the chromophores. Here, we present absorptive two-dimensional (2D) electronic spectra from living
cultures of the purple bacterium,
Rhodobacter sphaeroides
, acquired using gradient assisted photon
echo spectroscopy
.
Diagonal slices through the 2D lineshape of the LH1 stimulated emission/ground
state bleach feature reveal a resolvable higher energy population within the B875 manifold. The
waiting time evolution of diagonal, horizontal, and vertical slices through the 2D lineshape shows
a sub-100 fs intra-complex relaxation as this higher energy population red shifts. The absorption
(855 nm) of this higher lying sub-population of B875 before it has red shifted optimizes spectral
overlap between the LH1 B875 band and the B850 band of LH2. Access to an energetically broad
distribution of excitonic states within B875 offers a mechanism for efficient energy transfer from LH2
to LH1 during photosynthesis while limiting back transfer. Two-dimensional lineshapes reveal a rapid
decay in the ground-state bleach/stimulated emission of B875. This signal, identified as a decrease
in the dipole strength of a strong transition in LH1 on the red side of the B875 band, is assigned to
the rapid localization of an initially delocalized exciton state, a dephasing process that frustrates back
transfer from LH1 to LH2
Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle
We present an investigation of many-particle quantum walks in systems of
non-interacting distinguishable particles. Along with a redistribution of the
many-particle density profile we show that the collective evolution of the
many-particle system resembles the single-particle quantum walk evolution when
the number of steps is greater than the number of particles in the system. For
non-uniform initial states we show that the quantum walks can be effectively
used to separate the basis states of the particle in position space and
grouping like state together. We also discuss a two-particle quantum walk on a
two- dimensional lattice and demonstrate an evolution leading to the
localization of both particles at the center of the lattice. Finally we discuss
the outcome of a quantum walk of two indistinguishable particles interacting at
some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be
published in Quantum Information Processin
Skyrmion Excitations in Quantum Hall Systems
Using finite size calculations on the surface of a sphere we study the
topological (skyrmion) excitation in quantum Hall system with spin degree of
freedom at filling factors around . In the absence of Zeeman energy, we
find, in systems with one quasi-particle or one quasi-hole, the lowest energy
band consists of states with , where and are the total orbital and
spin angular momentum. These different spin states are almost degenerate in the
thermodynamic limit and their symmetry-breaking ground state is the state with
one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion
size is determined by the interplay of the Zeeman energy and electron-electron
interaction and the skyrmion shrinks to a spin texture of finite size. We have
calculated the energy gap of the system at infinite wave vector limit as a
function of the Zeeman energy and find there are kinks in the energy gap
associated with the shrinking of the size of the skyrmion. breaking ground
state is the state with one skyrmion of infinite size. In the presence of
Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman
energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques
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