14,419 research outputs found
Magnetic Phases in Dense Quark Matter
In this paper I discuss the magnetic phases of the three-flavor color
superconductor. These phases can take place at different field strengths in a
highly dense quark system. Given that the best natural candidates for the
realization of color superconductivity are the extremely dense cores of neutron
stars, which typically have very large magnetic fields, the magnetic phases
here discussed could have implications for the physics of these compact
objects.Comment: Presented at VII Latin American Symposium on Nuclear Physics and
Applications, El Cusco, Peru, June 200
Massive neutrinos and dark energy
We consider the impact of the Heidelberg-Moscow claim for a detection of
neutrino mass on the determination of the dark energy equation of state. By
combining the Heidelberg-Moscow result with the WMAP 3-years data and other
cosmological datasets we constrain the equation of state to -1.67< w <-1.05 at
95% c.l., While future data are certainly needed for a confirmation of the
controversial Heildelberg-Moscow claim, our result shows that future laboratory
searches for neutrino masses may play a crucial role in the determination of
the dark energy properties.Comment: 3 pages, 1 figure, Talk given by Paolo Serra at the Neutrino
Oscillation Workshop NOW2006, Otranto, Italy, September 9-16 200
Pulsed quantum optomechanics
Studying mechanical resonators via radiation pressure offers a rich avenue
for the exploration of quantum mechanical behavior in a macroscopic regime.
However, quantum state preparation and especially quantum state reconstruction
of mechanical oscillators remains a significant challenge. Here we propose a
scheme to realize quantum state tomography, squeezing and state purification of
a mechanical resonator using short optical pulses. The scheme presented allows
observation of mechanical quantum features despite preparation from a thermal
state and is shown to be experimentally feasible using optical microcavities.
Our framework thus provides a promising means to explore the quantum nature of
massive mechanical oscillators and can be applied to other systems such as
trapped ions.Comment: 9 pages, 4 figure
The "Unfriending" Problem: The Consequences of Homophily in Friendship Retention for Causal Estimates of Social Influence
An increasing number of scholars are using longitudinal social network data
to try to obtain estimates of peer or social influence effects. These data may
provide additional statistical leverage, but they can introduce new inferential
problems. In particular, while the confounding effects of homophily in
friendship formation are widely appreciated, homophily in friendship retention
may also confound causal estimates of social influence in longitudinal network
data. We provide evidence for this claim in a Monte Carlo analysis of the
statistical model used by Christakis, Fowler, and their colleagues in numerous
articles estimating "contagion" effects in social networks. Our results
indicate that homophily in friendship retention induces significant upward bias
and decreased coverage levels in the Christakis and Fowler model if there is
non-negligible friendship attrition over time.Comment: 26 pages, 4 figure
Dark Matter from the Inflaton Field
We present a model where inflation and Dark Matter takes place via a single
scalar field phi. Without introducing any new parameters we are able unify
inflation and Dark Matter using a scalar field phi that accounts for inflation
at an early epoch while it gives a Dark Matter WIMP particle at low energies.
After inflation our universe must be reheated and we must have a long period of
radiation dominated before the epoch of Dark Matter. Typically the inflaton
decays while it oscillates around the minimum of its potential. If the inflaton
decay is not complete or sufficient then the remaining energy density of the
inflaton after reheating must be fine tuned to give the correct amount of Dark
Matter. An essential feature here, is that Dark Matter-Inflaton particle is
produced at low energies without fine tuning or new parameters. This process
uses the same coupling g as for the inflaton decay. Once the field phi becomes
non-relativistic it will decouple as any WIMP particle, since n_phi is
exponentially suppressed. The correct amount of Dark Matter determines the
cross section and we have a constraint between the coupling and the mass
of phi. The unification scheme we present here has four free parameters,
two for the scalar potential V(phi) given by the inflation parameter lambda of
the quartic term and the mass m_o. The other two parameters are the coupling
between the inflaton phi and a scalar filed varphi and the coupling h
between varphi with standard model particles psi or chi. These four parameters
are already present in models of inflation and reheating process, without
considering Dark Matter. Therefore, our unification scheme does not increase
the number of parameters and it accomplishes the desired unification between
the inflaton and Dark Matter for free.Comment: 9 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:0911.517
The effects of short-term omission of daily medication on the pathophysiology of heart failure
Aims Pharmacological therapies for heart failure (HF) aim to improve congestion, symptoms, and prognosis. Failing to take medication is a potential cause of worsening HF. Characterizing the effects of short-term medication omission could inform the development of better technologies and strategies to detect and interpret the reasons for worsening HF. We examined the effect of planned HF medication omission for 48 h on weight, echocardiograms, transthoracic bio-impedance, and plasma concentrations of NT-proBNP. Methods and results Outpatients with stable HF and an LVEF <45% were assigned to take or omit their HF medication for 48 h in a randomized, crossover trial. Twenty patients (16 men, LVEF 32 ± 9%, median NT-proBNP 962 ng/L) were included. Compared with regular medication, omission led to an increase in NT-proBNP by 99% (from 962 to 1883 ng/L, P < 0.001), systolic blood pressure by 16% (from 131 to 152 mmHg, P < 0.001), and left atrial volume by 21% (from 69 to 80 mL, P = 0.001), and reductions in transthoracic bio-impedance by 10% (from 33 to 30 Σ, P = 0.001) and serum creatinine by 8% (from 135 to 118 µmol/L, P = 0.012). No significant changes in body weight, heart rate, or LVEF were observed. Conclusions The characteristic pattern of response to short-term medication omission is of increasing congestion but, in contrast to the pattern reported for disease progression, with a rise in blood pressure and improved renal function. In stable HF, weight is not a sensitive marker of short-term diuretic omission
Blockchain Application Within a Multi-Sensor Satellite Architecture
With the thrust towards multi-sensor satellite architectures for earth and space exploration, such as constellations and swarms, new technologies are required to enable the transition to this future capability. One of the areas of interest is establishing secure, efficient and prioritized data and command communication pathways among ground and space-based sources for such systems. This paper presents early research results on the potential role, capabilities and value of blockchain usage within constellation and swarm satellite architectures. It demonstrates the use of blockchain's smart contract and distributed ledger capabilities for secure and prioritized multi-sensor satellite collaborative data exchanges, as well as the logging and tracking of command and control events. Adapting and utilizing this emerging technology will aid in addressing technology gaps expected from future constellation flight architectures, such as managing collective computational operations (correlation), dynamic and autonomous observation planning, time-critical events, and provenance tied to ground and space-based autonomous operations and control recordkeeping. In this scenario blockchain is applied in encrypted command transmittal to multiple, yet specific, entities enabling acknowledgement transmittals, performance scalability, and automatic event-based triggering
Prevalence and Predictors of Vitamin D Insufficiency in Children: A Great Britain Population Based Study
Objectives
To evaluate the prevalence and predictors of vitamin D insufficiency (VDI) in children In Great Britain.
Design
A nationally representative cross-sectional study survey of children (1102) aged 4–18 years (999 white, 570 male) living in private households (January 1997–1998). Interventions provided information about dietary habits, physical activity, socio-demographics, and blood sample. Outcome measures were vitamin D insufficiency (<50 nmol/L).
Results
Vitamin D levels (mean = 62.1 nmol/L, 95%CI 60.4–63.7) were insufficient in 35%, and decreased with age in both sexes (p<0.001). Young People living between 53–59 degrees latitude had lower levels (compared with 50–53 degrees, p = 0.045). Dietary intake and gender had no effect on vitamin D status. A logistic regression model showed increased risk of VDI in the following: adolescents (14–18 years old), odds ratio (OR) = 3.6 (95%CI 1.8–7.2) compared with younger children (4–8 years); non white children (OR = 37 [95%CI 15–90]); blood levels taken December-May (OR = 6.5 [95%CI 4.3–10.1]); on income support (OR = 2.2 [95%CI 1.3–3.9]); not taking vitamin D supplementation (OR = 3.7 [95%CI 1.4–9.8]); being overweight (OR 1.6 [95%CI 1.0–2.5]); <1/2 hour outdoor exercise/day/week (OR = 1.5 [95%CI 1.0–2.3]); watched >2.5 hours of TV/day/week (OR = 1.6[95%CI 1.0–2.4]).
Conclusion
We confirm a previously under-recognised risk of VDI in adolescents. The marked higher risk for VDI in non-white children suggests they should be targeted in any preventative strategies. The association of higher risk of VDI among children who exercised less outdoors, watched more TV and were overweight highlights potentially modifiable risk factors. Clearer guidelines and an increased awareness especially in adolescents are needed, as there are no recommendations for vitamin D supplementation in older children
BDM Dark Matter: CDM with a core profile and a free streaming scale
We present a new dark matter model BDM which is an hybrid between hot dark
matter HDM and cold dark matter CDM, in which the BDM particles behave as HDM
above the energy scale E_c and as CDM below this scale. Evolution of structure
formation is similar to that of CDM model but BDM predicts a nonvanishing free
streaming l_fs scale and a inner galaxy core radius r_core, both quantities
determined in terms of a single parameter E_c, which corresponds to the phase
transition energy scale of the subjacent elementary particle model. For
energies above E_c or for a scale factor a smaller then a_c, with a<a_c<a_{eq},
the particles are massless and rho redshifts as radiation. However, once the
energy becomes E\leq E_c or a>a_c then the BDM particles acquire a large mass
through a non perturbative mechanism, as baryons do, and rho redshifts as
matter with the particles having a vanishing velocity. Typical energies are
E_c=O(10-100) eV giving a l_fs \propto E_c^{-4/3}\lesssim Mpc and m_fs\propto
E_c^{-4}\lesssim 10^9 M\odot. A l_fs\neq 0, r_core\neq 0 help to resolve some
of the shortcomings of CDM such as overabundance substructure in CDM halos and
numerical fit to rotation curves in dwarf spheroidal and LSB galaxies. Finally,
our BDM model and the phase transition scale E_c can be derived from particle
physics.Comment: 7 pages, 8 figure
Gravity and the Quantum Vacuum Inertia Hypothesis
In previous work it has been shown that the electromagnetic quantum vacuum,
or electromagnetic zero-point field, makes a contribution to the inertial
reaction force on an accelerated object. We show that the result for inertial
mass can be extended to passive gravitational mass. As a consequence the weak
equivalence principle, which equates inertial to passive gravitational mass,
appears to be explainable. This in turn leads to a straightforward derivation
of the classical Newtonian gravitational force. We call the inertia and
gravitation connection with the vacuum fields the quantum vacuum inertia
hypothesis. To date only the electromagnetic field has been considered. It
remains to extend the hypothesis to the effects of the vacuum fields of the
other interactions. We propose an idealized experiment involving a cavity
resonator which, in principle, would test the hypothesis for the simple case in
which only electromagnetic interactions are involved. This test also suggests a
basis for the free parameter which we have previously defined to
parametrize the interaction between charge and the electromagnetic zero-point
field contributing to the inertial mass of a particle or object.Comment: 18 pages, no figures. Annalen der Physik, 2005, in press. New version
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