6,643 research outputs found
Higher dimensional thin-shell wormholes in Einstein-Yang-Mills-Gauss-Bonnet gravity
We present thin-shell wormhole solutions in Einstein-Yang-Mills-Gauss-Bonnet
(EYMGB) theory in higher dimensions d\geq5. Exact black hole solutions are
employed for this purpose where the radius of thin-shell lies outside the event
horizon. For some reasons the cases d=5 and d>5 are treated separately. The
surface energy-momentum of the thin-shell creates surface pressures to resist
against collapse and rendering stable wormholes possible. We test the stability
of the wormholes against spherical perturbations through a linear
energy-pressure relation and plot stability regions. Apart from this restricted
stability we investigate the possibility of normal (i.e. non-exotic) matter
which satisfies the energy conditions. For negative values of the Gauss-Bonnet
(GB) parameter we obtain such physical wormholes.Comment: 9 pages, 6 figures. Dedicated to the memory of Rev. Ibrahim Eken
(1927-2010) of Turke
Technical Development of a New Semispherical Radiofrequency Bipolar Device (RONJA): Ex Vivo and In Vivo Studies
The aim of this study is to inform about the development of a new semispherical surgical instrument for the bipolar multielectrode radiofrequency liver ablation. Present tools are universal; however they have several disadvantages such as ablation of healthy tissue, numerous needle punctures, and, therefore, longer operating procedure. Our newly designed and tested semispherical surgical tool can solve some of these disadvantages. By conducting an in vivo study on a set of 12 pigs, randomly divided into two groups, we have compared efficiency of the newly developed instrument with the commonly used device. Statistical analysis showed that there were no significant differences between the groups. On average, the tested instrument RONJA had shorter ablation time in both liver lobes and reduced the total operating time. The depth of the thermal alteration was on average 4 mm larger using the newly tested instrument. The new radiofrequency method described in this study could be used in open liver surgery for the treatment of small liver malignancies (up to 2 cm) in a single application with the aim of saving healthy liver parenchyma. Further experimental studies are needed to confirm these results before clinical application of the method in the treatment of human liver malignancies
Anisotropic low-temperature piezoresistance in (311)A GaAs two-dimensional holes
We report low-temperature resistance measurements in a modulation-doped,
(311)A GaAs two-dimensional hole system as a function of applied in-plane
strain. The data reveal a strong but anisotropic piezoresistance whose
magnitude depends on the density as well as the direction along which the
resistance is measured. At a density of cm and for a
strain of about applied along [01], e.g., the
resistance measured along this direction changes by nearly a factor of two
while the resistance change in the [33] direction is less than 10% and
has the opposite sign. Our accurate energy band calculations indicate a
pronounced and anisotropic deformation of the heavy-hole dispersion with
strain, qualitatively consistent with the experimental data. The extremely
anisotropic magnitude of the piezoresistance, however, lacks a quantitative
explanation.Comment: 4 pages. Submitted to Applied Physics Letter
Subwavelength atom localization via amplitude and phase control of the absorption spectrum
We propose a scheme for subwavelength localization of an atom conditioned
upon the absorption of a weak probe field at a particular frequency.
Manipulating atom-field interaction on a certain transition by applying drive
fields on nearby coupled transitions leads to interesting effects in the
absorption spectrum of the weak probe field. We exploit this fact and employ a
four-level system with three driving fields and a weak probe field, where one
of the drive fields is a standing-wave field of a cavity. We show that the
position of an atom along this standing wave is determined when probe field
absorption is measured. We find that absorption of the weak probe field at a
certain frequency leads to subwavelength localization of the atom in either of
the two half-wavelength regions of the cavity field by appropriate choice of
the system parameters. We term this result as sub-half-wavelength localization
to contrast it with the usual atom localization result of four peaks spread
over one wavelength of the standing wave. We observe two localization peaks in
either of the two half-wavelength regions along the cavity axis.Comment: Accepted for publication to Physical Review
Solutions for f(R) gravity coupled with electromagnetic field
In the presence of external, linear / nonlinear electromagnetic fields we
integrate f(R) \sim R+2{\alpha}\surd(R+const.) gravity equations. In contrast
to their Einsteinian cousins the obtained black holes are non-asymptotically
flat with a deficit angle. In proper limits we obtain from our general solution
the global monopole solution in f(R) gravity. The scale symmetry breaking term
adopted as the nonlinear electromagnetic source adjusts the sign of the mass of
the resulting black hole to be physical.Comment: 7 pages no figure, final version for publication in European Physical
Journal
The Quantum Emergence of Chaos
The dynamical status of isolated quantum systems, partly due to the linearity
of the Schrodinger equation is unclear: Conventional measures fail to detect
chaos in such systems. However, when quantum systems are subjected to
observation -- as all experimental systems must be -- their dynamics is no
longer linear and, in the appropriate limit(s), the evolution of expectation
values, conditioned on the observations, closely approaches the behavior of
classical trajectories. Here we show, by analyzing a specific example, that
microscopic continuously observed quantum systems, even far from any classical
limit, can have a positive Lyapunov exponent, and thus be truly chaotic.Comment: 4 pages, 4 figure
Observation of Individual Josephson Vortices in YBCO Bicrystal Grain-boundary Junctions
The response of YBCO bicrystal grain-boundary junctions to small dc magnetic
fields (0 - 10 Oe) has been probed with a low-power microwave (rf) signal of
4.4 GHz in a microwave-resonator setup. Peaks in the microwave loss at certain
dc magnetic fields are observed that result from individual Josephson vortices
penetrating into the grain-boundary junctions under study. The system is
modeled as a long Josephson junction described by the sine-Gordon equation with
the appropriate boundary conditions. Excellent quantitative agreement between
the experimental data and the model has been obtained. Hysteresis effect of dc
magnetic field is also studied and the results of measurement and calculation
are compared.Comment: 11 pages, 4 figure
Perancangan Ulang Instalasi Pengolahan Air Limbah Domestik dengan Proses Anaerobic Baffled Reactor dan Anaerobic Filter
Instalasi Pengolahan Air Limbah (IPAL) Tarbiyatul Fallah merupakan IPAL domestik yang melayani Pesantren Tarbiyatul Fallah, namun berhenti beroperasi sejak tahun 2014. Agar manfaat IPAL dapat terus dirasakan, dilakukan perancangan ulang IPAL dengan alternatif Anaerobic Baffled Reactor (ABR) dan Anaerobic Filter (AF). Alternatif IPAL anaerobik yang keunggulan dalam kemudahan penerapan dan biaya operasional yang rendah. Perancangan ulang dimulai dengan mengevaluasi kinerja IPAL yang sudah ada. Hasil evaluasi digunakan untuk mengetahui permasalahan IPAL. Kemudian dilakukan perencanaan aternatif IPAL dengan proses ABR dan AF. Hasil perencanaan adalah berupa DED, BOQ, dan RAB pembangunan dan operasional. Berdasarkan hasil tersebut kemudian dibandingkan kelebihan dan kekurangan dari masing-masing alternatif IPAL. IPAL Tarbiyatul Fallah berhenti beroperasi disebabkan oleh permasalahan bau dan suara bising dari proses aerasi yang meresahkan masyarakat dan biaya operasional yang tinggi. Alternatif IPAL pengganti dapat berupa ABR dengan dimensi (15,1 m x 1,9 m x 2,3 m) dan AF dengan dimensi (13,75 m x 2,4 m x 2,3 m). Biaya pembangunan untuk ABR sebesar Rp152.969.500 dan AF sebesar Rp175.140.500. Sedangkan biaya operasional ABR sebesar Rp17.012.400 per tahun dan AF sebesar Rp21.345.950 per tahun. ABR memiliki keunggulan dalam hal tingkat penyisihan polutan, waktu tinggal, luas lahan dan biaya pembangunan dan operasional dibanding AF. Sedangkan AF memiliki keunggulan dalam jumlah kompartemen dan kebutuhan beton yang dibanding ABR
Fresh inflation and decoherence of super Hubble fluctuations
I study a stochastic approach to the recently introduced fresh inflation
model for super Hubble scales. I find that the state loses its coherence at the
end of the fresh inflationary period as a consequence of the damping of the
interference function in the reduced density matrix. This fact should be a
consequence of a) the relative evolutions of both the scale factor and the
horizon and b) the additional thermal and dissipative effects. This implies a
relevant difference with respect to supercooled inflationary scenarios which
require a very rapid expansion of the scale factor to give the decoherence of
super Hubble fluctuations.Comment: version with minor changes. To appear in Phys. Rev.
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