584 research outputs found
Spontaneous patterns in coherently driven polariton microcavities
We consider a polariton microcavity resonantly driven by two external lasers
which simultaneously pump both lower and upper polariton branches at normal
incidence. In this setup, we study the occurrence of instabilities of the
pump-only solutions towards the spontaneous formation of patterns. Their
appearance is a consequence of the spontaneous symmetry breaking of
translational and rotational invariance due to interaction induced parametric
scattering. We observe the evolution between diverse patterns which can be
classified as single-pump, where parametric scattering occurs at the same
energy as one of the pumps, and as two-pump, where scattering occurs at a
different energy. For two-pump instabilities, stripe and chequerboard patterns
become the dominant steady-state solutions because cubic parametric scattering
processes are forbidden. This contrasts with the single-pump case, where
hexagonal patterns are the most common arrangements. We study the possibility
of controlling the evolution between different patterns. Our results are
obtained within a linear stability analysis and are confirmed by finite size
full numerical calculations.Comment: 15 pages, 9 figure
Review of free-space optical communications with diverging beam
The report reviews the technology of Free-space Optical Communication (FSO) and simulation methods for testing the performance of diverged beam in the technology. In addition to the introduction, the theory of turbulence and its effect over laser is also reviewed. In the simulation revision chapter, on-off keying (OOK) and diverged beam is assumed in the transmitter, and in the receiver, avalanche photodiode (APD) is utilized to convert the photon stream into electron stream. Phase screens are adopted to simulate the effect of turbulence over the phase of the optical beam. Apart from this, the method of data processing is introduced and retrospected. In the summary chapter, there is a general explanation of different beam divergence and their performance
High Power and Optomechanics in Advanced LIGO Detectors
In September 2015, a new era of astronomy began with the first direct detection of grav- itational waves from a binary black hole coalescence. The event was captured by the Laser Interferometer Gravitational-wave Observatory, comprised of two long-baseline interferometers, one in Livingston, LA and one in Hanford, WA. At the time of the first detection, the interferometers were part way through an upgrade to an advanced configuration and were operating with a strain sensitivity of just better than 10−23/Hz1/2 around 100Hz. The full Advanced LIGO design calls for sensitivity of a few parts in 10−24/Hz1/2.
This thesis covers the detector upgrade to double the input power, thereby reducing quantum shot noise, which currently limits LIGO strain sensitivity above 100Hz. First, it presents the design of the interferometer and the noises – fundamental, technical, and environmental – which contribute to the full sensitivity curve, motivating the need for high power. The details of the high power laser upgrade are discussed. Second, it presents select side effects of high power, which can result in overall losses and heighten specific classical noise couplings. The work particularly focuses on a three-mode opto-mechanical interaction that can become unstable at high power, threatening the operational ability of the detector; multiple successful mitigation technique are presented and compared.
The results of this work, combined with the collaborative work of many others, allow the Advanced LIGO detectors to achieve a strain sensitivity better than 5 × 10−24/Hz1/2 during the third observation run
Microscopic insights on field induced switching and domain wall motion in orthorhombic ferroelectrics
Surprisingly little is known about the microscopic processes that govern
ferroelectric switching in orthorhombic ferroelectrics.
To study microscopic switching processes we combine ab initio-based molecular
dynamics simulations and data science on the prototypical material BaTiO.
We reveal two different field regimes: For moderate field strengths, the
switching is dominated by domain wall motion while a fast bulk-like switching
can be induced for large fields. Switching in both field regimes follows a
multi-step process via polarization directions perpendicular to the applied
field. In the former case, the moving wall is of Bloch character and hosts
dipole vortices due to nucleation, growth, and crossing of two dimensional
90 domains. In the second case, the local polarization shows a
continuous correlated rotation via a an intermediate tetragonal multidomain
state.Comment: 12 pages, 14 figure
Power saving and optimal hybrid precoding in millimeter wave massive MIMO systems for 5G
The proliferation of wireless services emerging from use cases offifth-generation(5G) technology is posing many challenges on cellular communicationinfrastructure. They demand to connect a massive number of devices withenhanced data rates. The massive multiple-input multiple-output (MIMO)technology at millimeter-wave (mmWave) in combination with hybrid precodingemerges as a concrete tool to address the requirements of 5G networkdevelopments. But Massive MIMO systems consume significant power fornetwork operations. Hence the prior role is to improve the energy efficiency byreducing the power consumption. This paper presents the power optimizationmodels for massive MIMO systems considering perfect channel state information(CSI) and imperfect CSI. Further, this work proposes an optimal hybrid precodingsolution named extended simultaneous orthogonal matchingpursuit (ESOMP).Simulation results reveal that a constant sum-rate can be achieved in massiveMIMO systems while significantly reducing the power consumption. Theproposed extended SOMPhybrid precoder performsclose to the conventionaldigital beamforming method. Further, modulation schemes compatible withmassive MIMO systems are outlined and their bit error rate (BER) performance isinvestigate
Multiparticle Dynamics 2004
We summarize results presented at this conference with special emphasis on
hard processes with jets and heavy quarks, soft particle production, small x
structure functions and diffraction as well as heavy ion collisions and quark
gluon plasma.Comment: Summary talk at XXXIV International Symposium on Multiparticle
Dynamics (ISMD 2004), Sonoma State University, Rohnert Park, California, July
26 - August 1, 2004, 21 pages, 4 figure
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