1,907 research outputs found
Optimal distinction between non-orthogonal quantum states
Given a finite set of linearly independent quantum states, an observer who
examines a single quantum system may sometimes identify its state with
certainty. However, unless these quantum states are orthogonal, there is a
finite probability of failure. A complete solution is given to the problem of
optimal distinction of three states, having arbitrary prior probabilities and
arbitrary detection values. A generalization to more than three states is
outlined.Comment: 9 pages LaTeX, one PostScript figure on separate pag
Convex probability domain of generalized quantum measurements
Generalized quantum measurements with N distinct outcomes are used for
determining the density matrix, of order d, of an ensemble of quantum systems.
The resulting probabilities are represented by a point in an N-dimensional
space. It is shown that this point lies in a convex domain having at most d^2-1
dimensions.Comment: 7 pages LaTeX, one PostScript figure on separate pag
On the differences between bubble-mediated air-water transfer in freshwater and seawater
Bubble populations and gas transfer velocities were measured in cleaned and surfactant-influenced freshwater and seawater. A nonlinear fitting technique was used to partition the total gas transfer velocity for a gas in each water type into a turbulence- and bubble-mediated fraction. This showed that the bubble-mediated transfer fraction was larger in cleaned freshwater than in cleaned seawater and that the difference was a function of diffusivity and solubility. This was explained by the fact that the bubble measurements showed that bubble plumes in cleaned freshwater had a higher concentration of large bubbles and a lower concentration of small bubbles than the plumes in cleaned seawater. The differences between the behavior of the bubble-mediated gas flux in cleaned freshwater and cleaned seawater show that caution should be used when intercomparing laboratory results from measurements made in different media. These differences also will make parameterizations of bubble-mediated gas exchange developed using freshwater laboratory data difficult to apply directly to oceanic conditions. It was found that adding a surfactant to seawater had minimal impact on the concentration of bubbles in the plumes. Because surfactants decrease the gas flux to the individual bubbles, the similarity in bubble population meant that the addition of surfactant to seawater decreased the bubble-mediated gas flux compared to the flux in cleaned seawater. In contrast, the addition of a surfactant to freshwater increased the concentration of bubbles by over an order of magnitude. This increase in bubble population was large enough to offset the decrease in the flux to the individual bubbles so that the net bubble-mediated gas flux in freshwater increased when surfactant was added. This difference in behavior of the bubble population and bubble-mediated transfer velocity between surfactant-influenced and cleaned waters further complicates interrelating laboratory measurements and applying laboratory results to the ocean
The TRENDS High-Contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf
The mass and age of substellar objects are degenerate parameters leaving the
evolutionary state of brown dwarfs ambiguous without additional information.
Theoretical models are normally used to help distinguish between old, massive
brown dwarfs and young, low mass brown dwarfs but these models have yet to be
properly calibrated. We have carried out an infrared high-contrast imaging
program with the goal of detecting substellar objects as companions to nearby
stars to help break degeneracies in inferred physical properties such as mass,
age, and composition. Rather than using imaging observations alone, our targets
are pre-selected based on the existence of dynamical accelerations informed
from years of stellar radial velocity (RV) measurements. In this paper, we
present the discovery of a rare benchmark brown dwarf orbiting the nearby
( pc), solar-type (G9V) star HD 4747 ([Fe/H]=)
with a projected separation of only AU (
0.6"). Precise Doppler measurements taken over 18 years reveal the companion's
orbit and allow us to place strong constraints on its mass using dynamics (). Relative photometry (,
, ) indicates that HD 4747 B is
most-likely a late-type L-dwarf and, if near the L/T transition, an intriguing
source for studying cloud physics, variability, and polarization. We estimate a
model-dependent mass of for an age of
Gyr based on gyrochronology. Combining astrometric measurements with RV data,
we calculate the companion dynamical mass () and orbit
() directly. As a new mass, age, and metallicity benchmark, HD
4747 B will serve as a laboratory for precision astrophysics to test
theoretical models that describe the emergent radiation of brown dwarfs.Comment: Accepted to Ap
A condition for any realistic theory of quantum systems
In quantum physics, the density operator completely describes the state.
Instead, in classical physics the mean value of every physical quantity is
evaluated by means of a probability distribution. We study the possibility to
describe pure quantum states and events with classical probability
distributions and conditional probabilities and prove that the distributions
can not be quadratic functions of the quantum state. Some examples are
considered. Finally, we deal with the exponential complexity problem of quantum
physics and introduce the concept of classical dimension for a quantum system
Quantum State Disturbance vs. Information Gain: Uncertainty Relations for Quantum Information
When an observer wants to identify a quantum state, which is known to be one
of a given set of non-orthogonal states, the act of observation causes a
disturbance to that state. We investigate the tradeoff between the information
gain and that disturbance. This issue has important applications in quantum
cryptography. The optimal detection method, for a given tolerated disturbance,
is explicitly found in the case of two equiprobable non-orthogonal pure states.Comment: 20 pages, standard LaTeX, four png figures (also available from the
authors: [email protected] and [email protected]
A Third Planet Orbiting HIP 14810
We present new precision radial velocities and a three-planet Keplerian orbit
fit for the V = 8.5, G5 V star HIP 14810. We began observing this star at Keck
Observatory as part of the N2K Planet Search Project. Wright et al. (2007)
announced the inner two planets to this system, and subsequent observations
have revealed the outer planet planet and the proper orbital solution for the
middle planet. The planets have minimum masses of 3.9, 1.3, and 0.6 M_Jup and
orbital periods of 6.67, 147.7, and 952 d, respectively. We have numerically
integrated the family of orbital solutions consistent with the data and find
that they are stable for at least 10^6 yr. Our photometric search shows that
the inner planet does not transit.Comment: ApJL, accepte
A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass
We report precise Doppler measurements of GJ317 (M3.5V) that reveal the
presence of a planet with a minimum mass Msini = 1.2 Mjup in an eccentric,
692.9 day orbit. GJ317 is only the third M dwarf with a Doppler-detected Jovian
planet. The residuals to a single-Keplerian fit show evidence of a possible
second orbital companion. The inclusion of an additional Jupiter-mass planet (P
= 2700 days, Msini = 0.83 Mjup) improves the quality of fit significantly,
reducing the rms from 12.5 m/s to 6.32 m/s. A false-alarm test yields a 1.1%
probability that the curvature in the residuals of the single-planet fit is due
to random fluctuations, lending additional credibility to the two-planet model.
However, our data only marginally constrain a two-planet fit and further
monitoring is necessary to fully characterize the properties of the second
planet. To study the effect of stellar mass on Jovian planet occurrence we
combine our samples of M stars, Solar-mass dwarfs and intermediate-mass
subgiants. We find a positive correlation between stellar mass and the
occurrence rate of Jovian planets within 2.5 AU; the former A-type stars in our
sample are nearly 5 times more likely than the M dwarfs to harbor a giant
planet. Our analysis shows that the correlation between Jovian planet
occurrence and stellar mass remains even after accounting for the effects of
stellar metallicity.Comment: ApJ accepted, 27 pages, 6 figures, 3 table
Neoadjuvant chemotherapy and trastuzumab versus neoadjuvant chemotherapy followed by post-operative trastuzumab for patients with HER2-positive breast cancer
Neoadjuvant chemotherapy plus trastuzumab (NCT) increases the rate of pathological complete response (pCR) and event-free survival (EFS) compared to neoadjuvant chemotherapy (NC) alone in women with HER2 positive breast cancer (BC). pCR in this setting is associated with improved EFS. Whether NCT preferentially improves EFS in comparison to NC followed by adjuvant trastuzumab initiated postoperatively (NCAT) has not been addressed. Using clinical data from women with HER2 positive BC treated at 7 European institutions between 2007 and 2010 we sought to investigate the impact on breast cancer outcomes of concomitant (NCT) versus sequential (NCAT) treatment in HER2 positive early BC. The unadjusted hazard ratio (HR) for event free survival with NCT compared with NCAT was 0.63 (95% CI 0.37–1.08; p = 0.091). Multivariable analysis revealed that treatment group, tumour size and ER status were significantly associated with EFS from diagnosis. In the whole group NCT was associated with a reduced risk of an event relative to NCAT, an effect that was confined to ER negative (HR: 0.25; 95% CI, 0.10–0.62; p = 0.003) as opposed to ER positive tumours (HR: 1.07; 95% CI, 0.46–2.52; p = 0.869). HER2 positive/ER negative BC treated with NC gain greatest survival benefit when trastuzumab is administered in both the neoadjuvant and adjuvant period rather than in the adjuvant period alone. These data support the early introduction of targeted combination therapy in HER2 positive/ER negative BC
Quantum and classical descriptions of a measuring apparatus
A measuring apparatus is described by quantum mechanics while it interacts
with the quantum system under observation, and then it must be given a
classical description so that the result of the measurement appears as
objective reality. Alternatively, the apparatus may always be treated by
quantum mechanics, and be measured by a second apparatus which has such a dual
description. This article examines whether these two different descriptions are
mutually consistent. It is shown that if the dynamical variable used in the
first apparatus is represented by an operator of the Weyl-Wigner type (for
example, if it is a linear coordinate), then the conversion from quantum to
classical terminology does not affect the final result. However, if the first
apparatus encodes the measurement in a different type of operator (e.g., the
phase operator), the two methods of calculation may give different results.Comment: 18 pages LaTeX (including one encapsulated PostScript figure
- …