6,723 research outputs found
Reducing the linewidth of an atom laser by feedback
A continuous atom laser will almost certainly have a linewidth dominated by
the effect of the atomic interaction energy, which turns fluctuations in the
condensate atom number into fluctuations in the condensate frequency. These
correlated fluctuations mean that information about the atom number could be
used to reduce the frequency fluctuations, by controlling a spatially uniform
potential. We show that feedback based on a physically reasonable quantum
non-demolition measurement of the atom number of the condensate in situ can
reduce the linewidth enormously.Comment: 5 pages, 1 figur
Effects of twin-beam squashed light on a three-level atom
An electro-optical feedback loop can make in-loop light (squashed light)
which produces a photocurrent with noise below the standard quantum limit (such
as squeezed light). We investigate the effect of squashed light interacting
with a three-level atom in the cascade configuration and compare it to the
effects produced by squeezed light and classical noise. It turns out that one
master equation can be formulated for all three types of light and that this
unified formalism can also be applied to the evolution of a two-level atom. We
show that squashed light does not mimic all aspects of squeezed light, and in
particular, it does not produce the characteristic linear intensity dependence
of the population of the upper-most level of the cascade three-level atom.
Nevertheless, it has nonclassical transient effects in the de-excitation.Comment: 12 pages, 6 figure
Interaction between three subpopulations of Ehrlich carcinoma in mixed solid tumours in nude mice: evidence of contact domination.
Clonal interaction between three subpopulations of Ehrlich carcinoma were studied during growth as mixed solid tumours and as ascites tumours in immune-incompetent nude NMRI mice. The tumour cell lines differed in DNA content as determined by DNA flow cytometry (FCM). Tumour growth was evaluated by tumour growth curves including calculation of tumour volume doubling times, tumour weight on day 14, cell cycle times (per cent labelled mitoses) and cell cycle distributions (FCM). Two subpopulations (E1.15 and E1.95) showed nearly identical growth characteristics during both solid and ascites tumour growth. The third subpopulation (E1.80) grew more slowly. FCM on fine-needle tumour aspirates was used to determine the relative proportions of the cell populations in mixed solid tumours in which E1.95 showed a growth-dominating effect on E1.15. No such effect was demonstrated during single-cell tumour growth in ascitic fluid in which the cells had no intimate contact. Ascitic fluid from E1.95-bearing animals or radiation-killed E1.95 cells had no effect on the growth of E1.15, and no remote effect was seen when the two cell lines were growing in opposite flanks. This indicates that only viable E1.95 cells in close in vivo contact were able to induce growth inhibition of the E1.15 subpopulation. Both the E1.95 and the E1.15 cells dominated the E1.80 cells, but in these cases cell kinetic differences may have played a role as the E1.95 and the E1.15 lines grew faster than the E1.80. The E1.80 cell line had no dominating effect on the E1.15 or E1.95. It is concluded that non-immunologically mediated cellular dominance in heterogeneous tumours may contribute to the evolution of these tumours and may be involved in fundamental tumour biological phenomena
Pure-state quantum trajectories for general non-Markovian systems do not exist
Since the first derivation of non-Markovian stochastic Schr\"odinger
equations, their interpretation has been contentious. In a recent Letter [Phys.
Rev. Lett. 100, 080401 (2008)], Di\'osi claimed to prove that they generate
"true single system trajectories [conditioned on] continuous measurement". In
this Letter we show that his proof is fundamentally flawed: the solution to his
non-Markovian stochastic Schr\"odinger equation at any particular time can be
interpreted as a conditioned state, but joining up these solutions as a
trajectory creates a fiction.Comment: 4 page
States for phase estimation in quantum interferometry
Ramsey interferometry allows the estimation of the phase of rotation
of the pseudospin vector of an ensemble of two-state quantum systems. For
small, the noise-to-signal ratio scales as the spin-squeezing parameter
, with possible for an entangled ensemble. However states with
minimum are not optimal for single-shot measurements of an arbitrary
phase. We define a phase-squeezing parameter, , which is an appropriate
figure-of-merit for this case. We show that (unlike the states that minimize
), the states that minimize can be created by evolving an
unentangled state (coherent spin state) by the well-known 2-axis
counter-twisting Hamiltonian. We analyse these and other states (for example
the maximally entangled state, analogous to the optical "NOON" state ) using several different properties, including ,
, the coefficients in the pseudo angular momentum basis (in the three
primary directions) and the angular Wigner function . Finally
we discuss the experimental options for creating phase squeezed states and
doing single-shot phase estimation.Comment: 8 pages and 5 figure
Entanglement of two atomic samples by quantum non-demolition measurements
This paper presents simulations of the state vector dynamics for a pair of
atomic samples which are being probed by phase shift measurements on an optical
beam passing through both samples. We show how measurements, which are
sensitive to different atomic components, serve to prepare states which are
close to being maximally entangled.Comment: 8 pages, 8 figures, REVTeX
Expression of transforming growth factor beta (TGF beta) receptors and expression of TGF beta 1, TGF beta 2 and TGF beta 3 in human small cell lung cancer cell lines.
A panel of 21 small cell lung cancer cell (SCLC) lines were examined for the presence of Transforming growth factor beta receptors (TGF beta-r) and the expression of TGF beta mRNAs. By the radioreceptor assay we found high affinity receptors to be expressed in six cell lines. scatchard analysis of the binding data demonstrated that the cells bound between 4.5 and 27.5 fmol mg-1 protein with a KD ranging from 16 to 40 pM. TGF beta 1 binding to the receptors was confirmed by cross-linking TGF beta 1 to the TGF beta-r. Three classes of TGF beta-r were demonstrated, type I and type II receptors with M(r) = 65,000 and 90,000 and the betaglycan (type III) with M(r) = 280,000. Northern blotting showed expression of TGF beta 1 mRNA in ten, TGF beta 2 mRNA in two and TGF beta 3 mRNA in seven cell lines. Our results provide, for the first time, evidence that a large proportion of a broad panel of SCLC cell lines express TGF beta-receptors and also produce TGF beta mRNAs
Willmore minimizers with prescribed isoperimetric ratio
Motivated by a simple model for elastic cell membranes, we minimize the
Willmore functional among two-dimensional spheres embedded in R^3 with
prescribed isoperimetric ratio
Concurrent constraint programming with process mobility
We propose an extension of concurrent constraint programming with primitives for process migration within a hierarchical network, and we study its semantics. To this purpose, we first investigate a "pure " paradigm for process migration, namely a paradigm where the only actions are those dealing with transmissions of processes. Our goal is to give a structural definition of the semantics of migration; namely, we want to describe the behaviour of the system, during the transmission of a process, in terms of the behaviour of the components. We achieve this goal by using a labeled transition system where the effects of sending a process, and requesting a process, are modeled by symmetric rules (similar to handshaking-rules for synchronous communication) between the two partner nodes in the network. Next, we extend our paradigm with the primitives of concurrent constraint programming, and we show how to enrich the semantics to cope with the notions of environment and constraint store. Finally, we show how the operational semantics can be used to define an interpreter for the basic calculus.
VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50
We report the discovery of the gamma-ray burst GRB 000131 and its optical
afterglow. The optical identification was made with the VLT 84 hours after the
burst following a BATSE detection and an Inter Planetary Network localization.
GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal
62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m
follow-up observations. Broad-band and spectroscopic observations of the
spectral energy distribution reveals a sharp break at optical wavelengths which
is interpreted as a Ly-alpha absorption edge at 6700 A. This places GRB 000131
at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in
gamma rays alone was approximately 10^54 erg (depending on the assumed
cosmology). The rapid power-law decay of the afterglow (index alpha=2.25,
similar to bursts with a prior break in the lightcurve), however, indicates
collimated outflow, which relaxes the energy requirements by a factor of < 200.
The afterglow of GRB 000131 is the first to be identified with an 8-m class
telescope.Comment: 8 pages, 7 figures, accepted to A&A Letter
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