1,595 research outputs found
Unified Interacting Quark Stars in Regularized 4D Einstein Gauss-Bonnet Gravity
Since the derivation of a well-defined limit for 4D Einstein
Gauss-Bonnet (4DEGB) gravity coupled to a scalar field, there has been interest
in testing it as an alternative to Einstein's general theory of relativity.
Using the Tolman-Oppenheimer-Volkoff (TOV) equations modified for 4DEGB
gravity, we model the stellar structure of quark stars using a novel
interacting quark matter equation of state. We find that increasing the
Gauss-Bonnet coupling constant or the interaction parameter
both tend to increase the mass-radius profiles of quark stars described by this
theory, allowing a given central pressure to support larger quark stars in
general. These results logically extend to cases where , in which
increasing the magnitude of the interaction effects instead diminishes masses
and radii. We also analytically identify a critical central pressure in both
regimes, below which no quark star solutions exist due to the pressure function
having no roots. Most interestingly, we find that quark stars can exist below
the general relativistic Buchdahl bound and Schwarzschild radius , due to
the lack of a mass gap between black holes and compact stars in 4DEGB. Even for
small well within current observational constraints, we find that
quark star solutions in this theory can describe Extreme Compact Objects
(ECOs), objects whose radii are smaller than what is allowed by general
relativity
Novel Bio-Logging Tool for Studying Fine-Scale Behaviors of Marine Turtles in Response to Sound
Increases in the spatial scale and intensity of activities that produce marine anthropogenic sound highlight the importance of understanding the impacts and effects of sound on threatened species such as marine turtles. Marine turtles detect and behaviorally respond to low-frequency sounds, however few studies have directly examined their behavioral responses to specific types or intensities of anthropogenic or natural sounds. Recent advances in the development of bio-logging tools, which combine acoustic and fine-scale movement measurements, have allowed for evaluations of animal responses to sound. Here, we describe these tools and present a case study demonstrating the potential application of a newly developed technology (ROTAG, Loggerhead Instruments, Inc.) to examine behavioral responses of freely swimming marine turtles to sound. The ROTAG incorporates a three-axis accelerometer, gyroscope, and magnetometer to record the turtle\u27s pitch, roll, and heading; a pressure sensor to record turtle depth; a hydrophone to record the turtle\u27s received underwater acoustic sound field; a temperature gauge; and two VHF radio telemetry transmitters and antennas for tag and turtle tracking. Tags can be programmed to automatically release via a timed corrodible link several hours or days after deployment. We describe an example of the data collected with these tags and present a case study of a successful ROTAG deployment on a juvenile green turtle (Chelonia mydas) in the Paranaguá Estuary Complex, Brazil. The tag was deployed for 221 min, during which several vessels passed closely (\u3c2 km) by the turtle. The concurrent movement and acoustic data collected by the ROTAG were examined during these times to determine if the turtle responded to these anthropogenic sound sources. While fine-scale behavioral responses were not apparent (second-by-second), the turtle did appear to perform dives during which it remained still on or near the sea floor during several of the vessel passes. This case study provides proof of concept that ROTAGs can successfully be applied to free-ranging marine turtles to examine their behavioral response to sound. Finally, we discuss the broad applications that these tools have to study the fine-scale behaviors of marine turtles and highlight their use to aid in marine turtle conservation and management
M–M Bond-Stretching Energy Landscapes for M_2(dimen)_(4)^(2+) (M = Rh, Ir; dimen = 1,8-Diisocyanomenthane) Complexes
Isomers of Ir_2(dimen)_(4)^(2+) (dimen = 1,8-diisocyanomenthane) exhibit different Ir–Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir–Ir distance is favored at room temperature [K = ~8; ΔH° = −0.8 kcal/mol; ΔS° = 1.44 cal mol^(–1) K^(–1)]. We report calculations that shed light on M_2(dimen)_(4)^(2+) (M = Rh, Ir) structural differences: (1) metal–metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A_(2u)) distortion promotes twisting of the ligand backbone at short metal–metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir_2(dimen)_(4)^(2+) (4.1 Å Ir–Ir with 0° twist angle and ~3.6 Å Ir–Ir with ±12° twist angle) but not for the rhodium analogue (4.5 Å Rh–Rh with no twisting). Because both the ligand strain and A_(2u) distortional energy are virtually identical for the two complexes, the strength of the metal–metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir–Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir_2(dimen)_(4)^(2+) (R_(e,Ir–Ir) = 2.87 Å; F_(Ir–Ir) = 0.99 mdyn Å^(–1)); (2) a single-minimum, anharmonic surface for the ground state of Rh_2(dimen)_(4)^(2+) (R_(e,Rh–Rh) = 3.23 Å; F_(Rh–Rh) = 0.09 mdyn Å^(–1)); (3) a double-minimum (along the Ir–Ir coordinate) surface for the ground state of Ir_2(dimen)_(4)^(2+) (R_(e,Ir–Ir) = 3.23 Å; F_(Ir–Ir) = 0.16 mdyn Å^(–1))
Analog Particle Production Model for General Classes of Taub-NUT Black Holes
We derive a correspondence between the Hawking radiation spectra emitted from
general classes of Taub-NUT black holes with that induced by the relativistic
motion of an accelerated Dirichlet boundary condition (i.e.\ a perfectly
reflecting mirror) in (1+1)-dimensional flat spacetime. We demonstrate that the
particle and energy spectra is thermal at late-times and that particle
production is suppressed by the NUT parameter. We also compute the radiation
spectrum in the rotating, electrically charged (Kerr-Newman) Taub-NUT scenario,
and the extremal case, showing explicitly how these parameters affect the
outgoing particle and energy fluxes.Comment: 9+3 pages, 14 figure
Effects of Horizons on Entanglement Harvesting
We study the effects of horizons on the entanglement harvested between two
Unruh-DeWitt detectors via the use of moving mirrors with and without strict
horizons. The entanglement reveals the sensitivity of the entanglement
harvested to the global dynamics of the trajectories disclosing aspects of the
effect that global information loss (where incoming massless scalar field modes
from past null infinity cannot reach right future null infinity) has on local
particle detectors. We also show that entanglement harvesting is insensitive to
the sign of emitted radiation flux.Comment: Expanded discussions and added references. New appendix on numerical
convergence adde
Periodic and discrete Zak bases
Weyl's displacement operators for position and momentum commute if the
product of the elementary displacements equals Planck's constant. Then, their
common eigenstates constitute the Zak basis, each state specified by two phase
parameters. Upon enforcing a periodic dependence on the phases, one gets a
one-to-one mapping of the Hilbert space on the line onto the Hilbert space on
the torus. The Fourier coefficients of the periodic Zak bases make up the
discrete Zak bases. The two bases are mutually unbiased. We study these bases
in detail, including a brief discussion of their relation to Aharonov's modular
operators, and mention how they can be used to associate with the single degree
of freedom of the line a pair of genuine qubits.Comment: 15 pages, 3 figures; displayed abstract is shortened, see the paper
for the complete abstrac
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