619 research outputs found
Gravitational Radiation from First-Order Phase Transitions
It is believed that first-order phase transitions at or around the GUT scale
will produce high-frequency gravitational radiation. This radiation is a
consequence of the collisions and coalescence of multiple bubbles during the
transition. We employ high-resolution lattice simulations to numerically evolve
a system of bubbles using only scalar fields, track the anisotropic stress
during the process and evolve the metric perturbations associated with
gravitational radiation. Although the radiation produced during the bubble
collisions has previously been estimated, we find that the coalescence phase
enhances this radiation even in the absence of a coupled fluid or turbulence.
We comment on how these simulations scale and propose that the same enhancement
should be found at the Electroweak scale; this modification should make direct
detection of a first-order electroweak phase transition easier.Comment: 7 pages, 7 figure
Applications in Bioastronautics and Bioinformatics: Early Radiation Cataracts Detected by Noninvasive, Quantitative, and Remote Means
Human exploration of Mars is a key goal in NASA's exploration planning in the next 20 years. Maintaining crew health and good vision is certainly an important aspect of achieving a successful mission. Continuous radiation exposure is a risk factor for radiation-induced cataracts in astronauts because radiation exposure in space travel has the potential of accelerating the aging process (ref. 1). A patented compact device (ref. 2) based on the technique of dynamic light scattering (DLS) was designed for monitoring an astronaut's ocular health during long-duration space travel. This capability of early diagnosis, unmatched by any other clinical technique in use today, may enable prompt initiation of preventive/curative therapy. An Internet web-based system integrating photon correlation data and controlling the hardware to monitor cataract development in vivo at a remote site in real time (teleophthalmology) is currently being developed. The new technology detects cataracts very early (at the molecular level). Cataract studies onboard the International Space Station will be helpful in quantifying any adverse effect of radiation to ocular health. The normal lens in a human eye, situated behind the cornea, is a transparent tissue. It contains 35 wt % protein and 65 wt % water. Aging, disease (e.g., diabetes), smoking, dehydration, malnutrition, and exposure to ultraviolet light and ionizing radiation can cause agglomeration of the lens proteins. Protein aggregation can take place anywhere in the lens, causing lens opacity. The aggregation and opacification could produce nuclear (central portion of the lens) or cortical (peripheral) cataracts. Nuclear and posterior subcapsular (the membrane's capsule surrounds the whole lens) cataracts, being on the visual optical axis of the eye, cause visual impairment that can finally lead to blindness. The lens proteins, in their native state, are small in size. As a cataract develops, this size grows from a few nanometers (transparent) to several micrometers (cloudy). Ansari and Datiles have shown that DLS can detect cataracts at least two to three orders of magnitude earlier noninvasively and quantitatively than the best imaging (Scheimpflug) techniques in clinical use today (ref. 3)
Design and development of a low temperature, inductance based high frequency ac susceptometer
We report on the development of an induction based low temperature high
frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz
and at temperatures between 2 K and 300 K. Careful balancing of the detection
coils and calibration have allowed a sample magnetic moment resolution of
at 1 MHz. We will discuss the design and
characterization of the susceptometer, and explain the calibration process. We
also include some example measurements on the spin ice material CdErS
and iron oxide based nanoparticles to illustrate functionality
Researching the Aftermath of Slavery in Mainland East Africa: Methodological, Ethical, and Practical Challenges
This article examines ethical, practical, and methodological challenges in researching the aftermath of slavery in continental East Africa away from the coastal plantation belt. Interest in post-slavery there is recent and inspired by the apparent contrast with West Africa, where the issue is much more salient. The article explains this silence by highlighting politically-motivated avoidance of the issue in colonial sources and the preference of post-colonial historians for âusefulâ pasts. Further, it questions the balance of successful integration and continuing marginalization reflected in the apparent obsolescence of slavery. It argues that tracing the trajectories of ex-slaves requires attention to all forms of social inequality and dependency, to the potential status implications for informants of speaking about slavery, and to the variety of terms and fields of meaning relevant to freedom, unfreedom and dependency. Recent research in this vein shows that slave antecedents remain a matter of aibu, shame, and that ex-slavesâ disappearance as a social category took lifelong efforts on their part. While the social valence of slave antecedents is relatively limited in mainland East Africa, slavery remains a problematic and painful heritage that demands great circumspection by researchers
Homological Error Correction: Classical and Quantum Codes
We prove several theorems characterizing the existence of homological error
correction codes both classically and quantumly. Not every classical code is
homological, but we find a family of classical homological codes saturating the
Hamming bound. In the quantum case, we show that for non-orientable surfaces it
is impossible to construct homological codes based on qudits of dimension
, while for orientable surfaces with boundaries it is possible to
construct them for arbitrary dimension . We give a method to obtain planar
homological codes based on the construction of quantum codes on compact
surfaces without boundaries. We show how the original Shor's 9-qubit code can
be visualized as a homological quantum code. We study the problem of
constructing quantum codes with optimal encoding rate. In the particular case
of toric codes we construct an optimal family and give an explicit proof of its
optimality. For homological quantum codes on surfaces of arbitrary genus we
also construct a family of codes asymptotically attaining the maximum possible
encoding rate. We provide the tools of homology group theory for graphs
embedded on surfaces in a self-contained manner.Comment: Revtex4 fil
The discovery of polarization in the afterglow of GRB 990510 with the ESO Very Large Telescope
Following a BeppoSAX alert (Piro 1999a) and the discovery of the OT at SAAO
(Vreeswijk et al. 1999a), we observed GRB 990510 with the FORS instrument on
ESO's VLT Unit 1 (`Antu'). The burst is unremarkable in gamma rays, but in
optical is the first one to show good evidence for jet-like outflow (Stanek et
al. 1999, Harrison et al. 1999). We report the detection of significant linear
polarization in the afterglow: it is (1.6 +/- 0.2)% 0.86 days after trigger,
and after 1.81 days is consistent with that same value, but much more
uncertain. The polarization angle is constant on a time scale of hours, and may
be constant over one day. We conclude that the polarization is intrinsic to the
source and due to the synchrotron nature of the emission, and discuss the
random and ordered field geometries that may be responsible for it.Comment: submitted to ApJ Lett., 5 pages including 2 figures, uses
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Effect of the CRADLE vital signs alert device intervention on referrals for obstetric haemorrhage in low-middle income countries: a secondary analysis of a stepped- wedge cluster-randomised control trial.
BACKGROUND: Obstetric haemorrhage is the leading cause of maternal death worldwide, 99% of which occur in low and middle income countries. The majority of deaths and adverse events are associated with delays in identifying compromise and escalating care. Management of severely compromised pregnant women may require transfer to tertiary centres for specialised treatment, therefore early recognition is vital for efficient management. The CRADLE vital signs alert device accurately measures blood pressure and heart rate, calculates the shock index (heart rate divided by systolic blood pressure) and alerts the user to compromise through a traffic light system reflecting previously validated shock index thresholds. METHODS: This is a planned secondary analysis of data from the CRADLE-3 trial from ten clusters across Africa, India and Haiti where the device and training package were randomly introduced. Referral data were prospectively collected for a 4-week period before, and a 4-week period 3âmonths after implementation. Referrals from primary or secondary care facilities to higher level care for any cause were recorded. The denominator was the number of women seen for maternity care in these facilities. RESULTS: Between April 1 2016 and Nov 30th, 2017 536,223 women attended maternity care facilities. Overall, 3.7% (nâ=â2784/74,828) of women seen in peripheral maternity facilities were referred to higher level care in the control period compared to 4.4% (nâ=â3212/73,371) in the intervention period (OR 0.89; 0.39-2.05) (data for nine sites that were able to collect denominator). Of these 0.29% (nâ=â212) pre-intervention and 0.16% (nâ=â120) post-intervention were referred to higher-level facilities for maternal haemorrhage. Although overall referrals did not significantly reduce there was a significant reduction in referrals for obstetric haemorrhage (OR 0.56 (0.39-0.65) following introduction of the device with homogeneity (i-squared 26.1) between sites. There was no increase in any bleeding-related morbidity (maternal death or emergency hysterectomy). CONCLUSIONS: Referrals for obstetric haemorrhage reduced following implementation of the CRADLE Vital Signs Alert Device, occurring without an increase in maternal death or emergency hysterectomy. This demonstrates the potential benefit of shock index in management pathways for obstetric haemorrhage and targeting limited resources in low- middle- income settings. TRIAL REGISTRATION: This study is registered with the ISRCTN registry, number ISRCTN41244132 (02/02/2016)
Partitioning of on-demand electron pairs
We demonstrate the high fidelity splitting of electron pairs emitted on
demand from a dynamic quantum dot by an electronic beam splitter. The fidelity
of pair splitting is inferred from the coincidence of arrival in two detector
paths probed by a measurement of the partitioning noise. The emission
characteristic of the on-demand electron source is tunable from electrons being
partitioned equally and independently to electron pairs being split with a
fidelity of 90%. For low beam splitter transmittance we further find evidence
of pair bunching violating statistical expectations for independent fermions
Cosmology From Random Multifield Potentials
We consider the statistical properties of vacua and inflationary trajectories
associated with a random multifield potential. Our underlying motivation is the
string landscape, but our calculations apply to general potentials. Using
random matrix theory, we analyze the Hessian matrices associated with the
extrema of this potential. These potentials generically have a vast number of
extrema. If the cross-couplings (off-diagonal terms) are of the same order as
the self-couplings (diagonal terms) we show that essentially all extrema are
saddles, and the number of minima is effectively zero. Avoiding this requires
the same separation of scales needed to ensure that Newton's constant is stable
against radiative corrections in a string landscape. Using the central limit
theorem we find that even if the number of extrema is enormous, the typical
distance between extrema is still substantial -- with challenging implications
for inflationary models that depend on the existence of a complicated path
inside the landscape.Comment: revtex, 3 figures, 10 pages v2 refs adde
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