2,364 research outputs found
p-Adic Path Integrals for Quadratic Actions
The Feynman path integral in p-adic quantum mechanics is considered. The
probability amplitude
for one-dimensional systems with quadratic actions is calculated in an exact
form, which is the same as that in ordinary quantum mechanics.Comment: 9 page
Performance Improvement of QPSK Signal Predetection EGC Diversity Receiver
This paper proposes a modification of quadrature phase-shift-keying (QPSK) signal diversity reception with predetection equal gain combiner (EGC). The EGC combining is realized by using the constant modulus algorithm (CMA). Carrier synchronization is performed by the phase locked loop (PLL). Comparative analysis of the modified and ordinary diversity receiver in the presence of carrier frequency offset in the additive white Gaussian noise (AWGN) channel, as well as in Rician fading channel is shown. The proposed diversity receiver allows significant frequency offset compared to the diversity receiver that uses only PLL, and the error probability of the proposed receiver is very close to the error probability of the receiver with only PLL and zero frequency offset. The functionality of the proposed diversity receiver, as well as its properties is experimentally verified on a system based on universal software radio peripheral (USRP) hardware. The performed comparison confirms the expected behavior of the system
Education and Research in the SEENET-MTP Regional Framework for Higher Education in Physics
Southeastern European countries undergo significant changes in the
demand/supply ratio on the labour market and in the structure of professional
competences that are necessary for undertaking a professional activity. In
addition, brain-drain process and decrease of interest for a career in basic
sciences put many challenges for our community. Consequently, based on the
activity of the Southeastern European Network in Mathematical and Theoretical
Physics (SEENET MTP Network) in connecting groups and persons working in
mathematics and theoretical physics, we investigate specific qualifications
recognized in these fields in all the countries from the region, and the
related competences necessary for practicing the respective occupations. A list
of new possible occupations will be promoted for inclusion in the National
Qualifications Register for Higher Education. Finally, we analyze the vision
existing in this region on the higher education qualifications against the
European vision and experience, in particular in training of Master students,
PhD students, and senior teaching and research staff through the Network, i.e.
multilateral and bilateral programs.Comment: 6 pages, Talk given at 7th International Conference of the Balkan
Physical Union, Alexandruoplos, Greece, 9-13 September 2009. To be published
in AIP Conf.Pro
Zero Dimensional Field Theory of Tachyon Matter
The first issue about the object (now) called tachyons was published almost
one century ago. Even though there is no experimental evidence of tachyons
there are several reasons why tachyons are still of interest today, in fact
interest in tachyons is increasing. Many string theories have tachyons
occurring as some of the particles in the theory. In this paper we consider the
zero dimensional version of the field theory of tachyon matter proposed by A.
Sen. Using perturbation theory and ideas of S. Kar, we demonstrate how this
tachyon field theory can be connected with a classical mechanical system, such
as a massive particle moving in a constant field with quadratic friction. The
corresponding Feynman path integral form is proposed using a perturbative
method. A few promising lines for further applications and investigations are
noted.Comment: 2 pages, Talk presented at the 6th International Conference of Balkan
Physical Union - BPU6, Istanbul, Turkey, August 22-26. 200
High School Class for Gifted Pupils in Physics and Sciences and Pupils` Skills Measured by Standard and Pisa Test
The ``High school class for students with special abilities in physics`` was
founded in Nis, Serbia in 2003. The basic aim of this project has been
introducing a broadened curriculum of physics, mathematics, computer science,
as well as chemistry and biology. We present analysis of the pupils` skills in
solving rather problem oriented test, as PISA test, and compare their results
with the results of pupils who study under standard curricula. Analysis of
achievement data should clarify what are benefits of introducing in school
system track for gifted students. Additionally, item analysis helps in
understanding and improvement of learning strategies efficacy.Comment: 6 pages, Talk given at 7th International Conference of the Balkan
Physical Union, Alexandruoplos, Greece, 9-13 September 2009. To be published
in AIP Conf.Pro
Redundancy resolution in tasks with parametrizable uncertainty
Redundant robots motion planning and control in uncertain task is addressed by model-based approach. Instead of control and adapt the environment to the robot or apply a complex visual servoing system, we have modeled the redundancy resolution (RR) on the parameter spaces that quantify uncertainties of the task. A modeling tool was Successive Approximations (SA). It provides very advantageous properties: small computational effort and small model size, accurate output, extrapolation, and generalization across parameter set obtained by random addressing of the model. The task discussed is press loading with typical two-dimensional uncertainties in pick-up and unloading locations. The robot used is 4 DOF planar robot. The SA-based models of redundancy resolution in the 2D parameter spaces are highly efficient: for more that 30 times less computational efforts resulted in a zero end-point errors, regardless of the task uncertainty
Effects of Imperfect Reference Signal Recovery on Performance of SC and SSC Receivers over Generalized Fading Channels
This paper presents the study of the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch-and-stay combining (SSC) and multibranch selection combining (SC) receivers in a generalized - fading channel. The average BER of binary and quaternary phase shift keying (BPSK and QPSK) is derived under the assumption that the reference carrier signal is extracted from the received modulated signal. For SSC receiver the optimal switching threshold (in a minimum BER sense) is numerically evaluated. Hereby we determine and discuss the simultaneous influence of the average signal-to-noise ratio (SNR) per bit, fading severity, product phase-locked loop (PLL) bandwidthbit duration (B_LT_b), switching threshold of SSC and diversity order of SC on BER performance. The influence of B_LT_b in different channel conditions and modulation formats is pointed out. The numerical results are confirmed by computer simulations
Exact Site Percolation Thresholds Using the Site-to-Bond and Star-Triangle Transformations
I construct a two-dimensional lattice on which the inhomogeneous site
percolation threshold is exactly calculable and use this result to find two
more lattices on which the site thresholds can be determined. The primary
lattice studied here, the ``martini lattice'', is a hexagonal lattice with
every second site transformed into a triangle. The site threshold of this
lattice is found to be , while the others have and
. This last solution suggests a possible approach to establishing
the bound for the hexagonal site threshold, . To derive these
results, I solve a correlated bond problem on the hexagonal lattice by use of
the star-triangle transformation and then, by a particular choice of
correlations, solve the site problem on the martini lattice.Comment: 12 pages, 10 figures. Submitted to Physical Review
- …