1,566 research outputs found
Locking Local Oscillator Phase to the Atomic Phase via Weak Measurement
We propose a new method to reduce the frequency noise of a Local Oscillator
(LO) to the level of white phase noise by maintaining (not destroying by
projective measurement) the coherence of the ensemble pseudo-spin of atoms over
many measurement cycles. This scheme uses weak measurement to monitor the phase
in Ramsey method and repeat the cycle without initialization of phase and we
call, "atomic phase lock (APL)" in this paper. APL will achieve white phase
noise as long as the noise accumulated during dead time and the decoherence are
smaller than the measurement noise. A numerical simulation confirms that with
APL, Allan deviation is averaged down at a maximum rate that is proportional to
the inverse of total measurement time, tau^-1. In contrast, the current atomic
clocks that use projection measurement suppress the noise only down to the
level of white frequency, in which case Allan deviation scales as tau^-1/2.
Faraday rotation is one of the possible ways to realize weak measurement for
APL. We evaluate the strength of Faraday rotation with 171Yb+ ions trapped in a
linear rf-trap and discuss the performance of APL. The main source of the
decoherence is a spontaneous emission induced by the probe beam for Faraday
rotation measurement. One can repeat the Faraday rotation measurement until the
decoherence become comparable to the SNR of measurement. We estimate this
number of cycles to be ~100 cycles for a realistic experimental parameter.Comment: 18 pages, 7 figures, submitted to New Journal of Physic
Pyrochlore Antiferromagnet: A Three-Dimensional Quantum Spin Liquid
The quantum pyrochlore antiferromagnet is studied by perturbative expansions
and exact diagonalization of small clusters. We find that the ground state is a
spin-liquid state: The spin-spin correlation functions decay exponentially with
distance and the correlation length never exceeds the interatomic distance. The
calculated magnetic neutron diffraction cross section is in very good agreement
with experiments performed on Y(Sc)Mn2. The low energy excitations are
singlet-singlet ones, with a finite spin gap.Comment: 4 pages, 4 figure
Buffer gas induced collision shift for the Sr clock transition
Precision saturation spectroscopy of the is
performed in a vapor cell filled with various rare gas including He, Ne, Ar,
and Xe. By continuously calibrating the absolute frequency of the probe laser,
buffer gas induced collision shifts of kHz are detected with gas
pressure of 1-20 mTorr. Helium gave the largest fractional shift of . Comparing with a simple impact calculation and a
Doppler-limited experiment of Holtgrave and Wolf [Phys. Rev. A {\bf 72}, 012711
(2005)], our results show larger broadening and smaller shifting coefficient,
indicating effective atomic loss due to velocity changing collisions. The
applicability of the result to the optical lattice clock
transition is also discussed
Mineralized Matrix Production by Osteoblasts on Solid Titanium In Vitro
Rat bone marrow cells were cultured on solid commercially pure titanium discs. Extracellular matrix (ECM) formed by the cells and the ECM/metal interface developed were examined by both scanning and transmission electron microscopy. The ECM most intimately associated with the substratum comprised afibrillar calcium phosphate globular accretions produced by the colonizing osteoblasts. The presence of calcium and phosphorus was confirmed by energy dispersive X-ray analysis. This initial layer acted as a site of anchorage for collagen fibres, produced by the osteoblasts. However, flaps of tissue elaborated during the culture period and manually reflected created a tissue division immediately above the afibrillar layer which indicated that the latter was adherent to the underlying metal oxide surface. The collagen matrix, consisting of networks of fibres, became mineralized with time in culture and also enveloped osteocytes which possessed radiating cell processes to form a bone nodule. This in vitro study suggests that while a calcified matrix layer, produced by osteoblasts, may adhere to titanium surfaces, subsequently formed bone is separated from this layer by a zone rich in both proteoglycans (as demonstrated by ruthenium red staining) and collagen fibres
Deposition and Resorption of Calcified Matrix in Vitro by Rat Marrow Cells
Rat bone marrow derived cells were cultured using a-Minimal Essential Medium supplemented with antibiotics, ascorbic acid and !3-glycerphosphate in the presence of 10-8M dexamethasone, on polystyrene and hydrophilic fluorocarbon substrata for periods of 2 - 4 weeks. During this time, a large yield of bone nodules was achieved and the elaborated tissue was examined by both scanning and transmission electron microscopy. The matrix produced by the cells contacting the underlying substratum was an afibrillar, globular, calcified material which formed a layer approximately 0.5μm thick. The calcium and phosphorus content of this material was confirmed by energy dispersive X-ray dot mapping analysis. The collagenous matrix of the forming bone nodules was intimately associated with, and anchored to, this layer. The bulk of the bone nodule, above the interfacial zone, was of a normal appearance with osteocytes buried in a collagenous matrix exhibiting spheritic foci of mineralization. The cells, but not the extracellular matrix, of this culture were then removed using a trypsin citrate saline solution and the dishes containing these nodules reseeded with fresh bone marrow cells. These second stage cultures were maintained in supplemented medium, without dexamethasone. During this second period, osteoclasts resorbed both the afibrillar and collagen containing calcified matrices laid down in the first stage of the culture, producing characteristic scalloped osteoclast resorption lacunae
Pressure Induced Quantum Critical Point and Non-Fermi-Liquid Behavior in BaVS3
The phase diagram of BaVS3 is studied under pressure using resistivity
measurements. The temperature of the metal to nonmagnetic Mott insulator
transition decreases under pressure, and vanishes at the quantum critical point
p_cr=20kbar. We find two kinds of anomalous conducting states. The
high-pressure metallic phase is a non-Fermi liquid described by Delta rho = T^n
where n=1.2-1.3 at 1K < T < 60K. At p<p_cr, the transition is preceded by a
wide precursor region with critically increasing resistivity which we ascribe
to the opening of a soft Coulomb gap.Comment: 4 pages, 5 eps figures, problem with figure correcte
Circadian Organization in Hemimetabolous Insects
The circadian system of hemimetabolous insects is reviewed in respect to the locus of the circadian clock and multioscillatory organization. Because of relatively easy access to the nervous system, the neuronal organization of the clock system in hemimetabolous insects has been studied, yielding identification of the compound eye as the major photoreceptor for entrainment and the optic lobe for the circadian clock locus. The clock site within the optic lobe is inconsistent among reported species; in cockroaches the lobula was previously thought to be a most likely clock locus but accessory medulla is recently stressed to be a clock center, while more distal part of the optic lobe including the lamina and the outer medulla area for the cricket. Identification of the clock cells needs further critical studies. Although each optic lobe clock seems functionally identical, in respect to photic entrainment and generation of the rhythm, the bilaterally paired clocks form a functional unit. They interact to produce a stable time structure within individual insects by exchanging photic and temporal information through neural pathways, in which
serotonin and pigment-dispersing factor (PDF) are involved as chemical messengers. The mutual interaction also plays an important role in seasonal adaptation of the rhythm
Hubbard chains network on corner-sharing tetrahedra: origin of the heavy fermion state in LiV_2O_4
We investigate the Hubbard chains network model defined on corner-sharing
tetrahedra (the pyrochlore lattice) which is a possible microscopic model for
the heavy fermion state of LiV_2O_4. Based upon this model, we can explain
transport, magnetic, and thermodynamic properties of LiV_2O_4. We calculate the
spin susceptibility, and the specific heat coefficient, exploiting the Bethe
ansatz exact solution of the 1D Hubbard model and bosonization method. The
results are quite consistent with experimental observations. We obtain the
large specific heat coefficient .Comment: 5 pages, 2 figures, a postscript file of Figure 1 is not included, to
appear in Physical Review
Temperature dependent Eu 3d-4f X-ray Absorption and Resonant Photoemission Study of the Valence Transition in
We study the mixed valence transition ( 80 K) in
EuNi(SiGe) using Eu 3 X-ray absorption
spectroscopy (XAS) and resonant photoemission spectroscopy (RESPES). The
Eu and Eu main peaks show a giant resonance and the spectral
features match very well with atomic multiplet calculations. The spectra show
dramatic temperature ()-dependent changes over large energies (10 eV)
in RESPES and XAS. The observed non-integral mean valencies of 2.35
0.03 ( = 120 K) and 2.70 0.03 ( = 40 K) indicate homogeneous
mixed valence above and below . The redistribution between
Eu+ and Eu+ states is attributed to
a hybridization change coupled to a Kondo-like volume collapse.Comment: 4 pages, 3 figure
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