1,831 research outputs found
Optimal Quantum Measurements for Phase Estimation
Quantum information theory is applied to practical interferometer-based phase measurements to deduce the optimal phase measurement scheme with two optical modes. Optimal phase measurements, given ideal input states, reveal an asymptotic 1/n decrease in phase uncertainty Delta theta for n the mean photon number of the input state. In contradistinction to previous schemes for realizing the number-phase uncertainty limit, the 1/n limit achieved here is independent of the interferometer phase shift; prior information about the expected phase shift is not necessary to attain this limit. These results apply more generally to su(2) and so(3) phase parameter estimation
The Accelerations of Stars Orbiting the Milky Way's Central Black Hole
Recent measurements, of the velocities of stars near the center of the Milky
Way have provided the strongest evidence for the presence of a supermassive
black hole in a galaxy, but the observational uncertainties poorly constrain
many of the properties of the black hole. Determining the accelerations of
stars in their orbits around the center provides much more precise information
about the position and mass of the black hole. Here we report measurements of
the accelerations for three stars located ~0.005 pc from the central radio
source Sgr A*; these accelerations are comparable to those experienced by the
Earth as it orbits the Sun. These data increase the inferred minimum mass
density in the central region of the Galaxy by an order of magnitude relative
to previous results and localized the dark mass to within 0.05 +- 0.04 arcsec
of the nominal position of Sgr A*. In addition, the orbital period of one of
the observed stars could be as short as 15 years, allowing us the opportunity
in the near future to observe an entire period.Comment: To appear in September 21 2000 issue of Natur
Growth in solvable subgroups of GL_r(Z/pZ)
Let and let be a subset of \GL_r(K) such that is
solvable. We reduce the study of the growth of $A$ under the group operation to
the nilpotent setting. Specifically we prove that either $A$ grows rapidly
(meaning $|A\cdot A\cdot A|\gg |A|^{1+\delta}$), or else there are groups $U_R$
and $S$, with $S/U_R$ nilpotent such that $A_k\cap S$ is large and
$U_R\subseteq A_k$, where $k$ is a bounded integer and $A_k = \{x_1 x_2...b x_k
: x_i \in A \cup A^{-1} \cup {1}}$. The implied constants depend only on the
rank $r$ of $\GL_r(K)$.
When combined with recent work by Pyber and Szab\'o, the main result of this
paper implies that it is possible to draw the same conclusions without
supposing that is solvable.Comment: 46 pages. This version includes revisions recommended by an anonymous
referee including, in particular, the statement of a new theorem, Theorem
Super-resolving phase measurements with a multi-photon entangled state
Using a linear optical elements and post-selection, we construct an entangled
polarization state of three photons in the same spatial mode. This state is
analogous to a ``photon-number path entangled state'' and can be used for
super-resolving interferometry. Measuring a birefringent phase shift, we
demonstrate two- and three-fold improvements in phase resolution.Comment: 4 pages, 3 figure
The inevitable youthfulness of known high-redshift radio galaxies
Radio galaxies can be seen out to very high redshifts, where in principle
they can serve as probes of the early evolution of the Universe. Here we show
that for any model of radio-galaxy evolution in which the luminosity decreases
with time after an initial rapid increase (that is, essentially all reasonable
models), all observable high-redshift radio-galaxies must be seen when the
lobes are less than 10^7 years old. This means that high-redshift radio
galaxies can be used as a high-time-resolution probe of evolution in the early
Universe. Moreover, this result helps to explain many observed trends of
radio-galaxy properties with redshift [(i) the `alignment effect' of optical
emission along radio-jet axes, (ii) the increased distortion in radio
structure, (iii) the decrease in physical sizes, (iv) the increase in radio
depolarisation, and (v) the increase in dust emission] without needing to
invoke explanations based on cosmology or strong evolution of the surrounding
intergalactic medium with cosmic time, thereby avoiding conflict with current
theories of structure formation.Comment: To appear in Nature. 4 pages, 2 colour figures available on request.
Also available at http://www-astro.physics.ox.ac.uk/~km
Evaluation of wrist and hip sedentary behaviour and moderate-to-vigorous physical activity raw acceleration cutpoints in older adults
Wrist-based accelerometers are now common in assessing physical activity (PA) and sedentary behaviour (SB) in population-based studies, but there is a scarcity of raw acceleration cutpoints in older adults. The study aimed to determine and evaluate wrist-based GENEActiv (GA) and hip-based ActiGraph GT3X+ (AG) raw acceleration cutpoints for SB and moderate-to-vigorous PA (MVPA) in older adults ≥60 years of age. A laboratory-based calibration analyses of 34 healthy older adults involved receiver operator characteristic (ROC) curves to determine raw acceleration cutpoints for SB and MVPA. ROC analysis revealed an area under the curve (AUC) of 0.88 for GA SB and MVPA, and 0.90 for AG SB and 0.94 for AG MVPA. Sensitivity optimised SB and specificity optimised MVPA GA cutpoints of 57 mg and 104 mg, and AG cutpoints of 15 mg and 69 mg were also generated, respectively. Cross-validation analysis revealed moderate agreement for GA and AG SB cutpoints, and fair to substantial agreement for GA and AG MVPA cutpoints, respectively. The resultant cutpoints can classify older adults as engaging in SB or not engaging in MVPA but the sensitivity optimised SB cutpoints should be interpreted with a degree of caution due to their modest cross-validation results
HST imaging of the dusty filaments and nucleus swirl in NGC4696 at the centre of the Centaurus Cluster
Narrow-band HST imaging has resolved the detailed internal structure of the
10 kpc diameter H alpha+[NII] emission line nebulosity in NGC4696, the central
galaxy in the nearby Centaurus cluster, showing that the dusty, molecular,
filaments have a width of about 60pc. Optical morphology and velocity
measurements indicate that the filaments are dragged out by the bubbling action
of the radio source as part of the AGN feedback cycle. Using the drag force we
find that the magnetic field in the filaments is in approximate pressure
equipartition with the hot gas. The filamentary nature of the cold gas
continues inward, swirling around and within the Bondi accretion radius of the
central black hole, revealing the magnetic nature of the gas flows in massive
elliptical galaxies. HST imaging resolves the magnetic, dusty, molecular
filaments at the centre of the Centaurus cluster to a swirl around and within
the Bondi radius.This is the accepted manuscript. It is currently embargoed pending publication
Clonal karyotype evolution involving ring chromosome 1 with myelodysplastic syndrome subtype RAEB-t progressing into acute leukemia
s Karyotypic evolution is a well-known phenomenon in patients with malignant hernatological disorders during disease progression. We describe a 50-year-old male patient who had originally presented with pancytopenia in October 1992. The diagnosis of a myelodysplastic syndrome (MDS) FAB subtype RAEB-t was established in April 1993 by histological bone marrow (BM) examination, and therapy with low-dose cytosine arabinoside was initiated. In a phase of partial hernatological remission, cytogenetic assessment in August 1993 revealed a ring chromosome 1 in 13 of 21 metaphases beside BM cells with normal karyotypes {[}46,XY,r(1)(p35q31)/46,XY]. One month later, the patient progressed to an acute myeloid leukemia (AML), subtype M4 with 40% BM blasts and cytogenetic examination showed clonal evolution by the appearance of additional numerical aberrations in addition to the ring chromosome{[}46,XY,r(1),+8,-21/45,XY,r(1),+8,-21,-22/46, XY]. Intensive chemotherapy and radiotherapy was applied to induce remission in preparation for allogeneic bone marrow transplantation (BMT) from the patient's HLA-compatible son. After BMT, complete remission was clinically, hematologically and cytogenetically (normal male karyotype) confirmed. A complete hematopoietic chimerism was demonstrated. A relapse in January 1997 was successfully treated using donor lymphocyte infusion and donor peripheral blood stem cells (PB-SC) in combination with GM-CSF as immunostimulating agent in April 1997, and the patient's clinical condition remained stable as of January 2005. This is an interesting case of a patient with AML secondary to MDS. With the ring chromosome 1 we also describe a rare cytogenetic abnormality that predicted the poor prognosis of the patient, but the patient could be cured by adoptive immunotherapy and the application of donor's PB-SC. This case confirms the value of cytogenetic analysis in characterizing the malignant clone in hernatological neoplasias, the importance of controlling the quality of an induced remission and of the detection of a progress of the disease. Copyright (c) 2006 S. Karger AG, Basel
Magnetic support of the optical emission line filaments in NGC 1275
The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster,
is surrounded by a well-known giant nebulosity of emission-line filaments,
which are plausibly about >10^8 yr old. The filaments are dragged out from the
centre of the galaxy by the radio bubbles rising buoyantly in the hot
intracluster gas before later falling back. They act as dramatic markers of the
feedback process by which energy is transferred from the central massive black
hole to the surrounding gas. The mechanism by which the filaments are
stabilized against tidal shear and dissipation into the surrounding 4x10^7 K
gas has been unclear. Here we report new observations that resolve thread-like
structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc
wide. We conclude that magnetic fields in the threads, in pressure balance with
the surrounding gas, stabilize the filaments, so allowing a large mass of cold
gas to accumulate and delay star formation.Comment: Published in Nature, includes supplementary information, high
resolution images available at http://www-xray.ast.cam.ac.uk/papers/ngc1275
Ram pressure feeding super-massive black holes
When supermassive black holes at the center of galaxies accrete matter
(usually gas), they give rise to highly energetic phenomena named Active
Galactic Nuclei (AGN). A number of physical processes have been proposed to
account for the funneling of gas towards the galaxy centers to feed the AGN.
There are also several physical processes that can strip gas from a galaxy, and
one of them is ram pressure stripping in galaxy clusters due to the hot and
dense gas filling the space between galaxies. We report the discovery of a
strong connection between severe ram pressure stripping and the presence of AGN
activity. Searching in galaxy clusters at low redshift, we have selected the
most extreme examples of jellyfish galaxies, which are galaxies with long
tentacles of material extending for dozens of kpc beyond the galaxy disk. Using
the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of
the 7 galaxies of this sample host a central AGN, and two of them also have
galactic-scale AGN ionization cones. The high incidence of AGN among the most
striking jellyfishes may be due to ram pressure causing gas to flow towards the
center and triggering the AGN activity, or to an enhancement of the stripping
caused by AGN energy injection, or both. Our analysis of the galaxy position
and velocity relative to the cluster strongly supports the first hypothesis,
and puts forward ram pressure as another, yet unforeseen, possible mechanism
for feeding the central supermassive black hole with gas.Comment: published in Nature, Vol.548, Number 7667, pag.30
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