2,307 research outputs found
An Electronically Reconfigurable Patch Antenna Design for Polarization Diversity with Fixed Resonant Frequency
In this paper, an electronically polarization reconfigurable circular patch antenna with fixed resonant frequency operating at Wireless Local Area Network (WLAN) frequency band (2.4-2.48 GHz) is presented. The structure of the proposed design consists of a circular patch as a radiating element fed by coaxial probe, cooperated with four equal-length slits etched on the edge along x-axis and y-axis. A total of four switches was used and embedded across the slits at specific locations, thus controlled the length of the slits. By activating and deactivating the switches (ON and OFF) across the slits, the current on the patch is changed, thus modifying the electric field and polarization of the antenna. Consequently, the polarization excited by the proposed antenna can be switched into three types, either linear polarization, left-hand circular polarization or right-hand circular polarization. This paper proposes a simple approach that able to switch the polarizations and excited at the same operating frequency. Simulated and measured results of ideal case (using copper strip switches) and real case (using PIN diode switches) are compared and presented to demonstrate the performance of the antenna
Noncommutative spacetime symmetries: Twist versus covariance
We prove that the Moyal product is covariant under linear affine spacetime
transformations. From the covariance law, by introducing an -space
where the spacetime coordinates and the noncommutativity matrix components are
on the same footing, we obtain a noncommutative representation of the affine
algebra, its generators being differential operators in -space. As
a particular case, the Weyl Lie algebra is studied and known results for Weyl
invariant noncommutative field theories are rederived in a nutshell. We also
show that this covariance cannot be extended to spacetime transformations
generated by differential operators whose coefficients are polynomials of order
larger than one. We compare our approach with the twist-deformed enveloping
algebra description of spacetime transformations.Comment: 19 pages in revtex, references adde
Using durian rind as bridging material to overcome fluid loss and lost circulation problems in drilling operations
Lost circulation is one of the drilling operational problems. It refers to the total or partial loss of drilling fluid into highly permeable zones or natural or induced fractures. This problem is likely to occur when the hydrostatic head pressure of drilling fluid in the hole exceeds the formation pressure. Today, managing lost circulation remains a significant challenge to oilwell drilling operations because it may contribute to high non-productive time. It is imperative to note that the overbalance pressure situation also can cause the invasion of mud filtrate into production zones which will result in formation damage. To address these problems, an experimental investigation has been done on durian rind as an alternative fluid loss and lost circulation materials in water-based mud. Durian rind was selected as a mud loss control material because it contains close to 20% pectin which may complement the formation of high quality mat-like bridges across openings of the formation. The test involved the use of standard mud testing equipment and a lost circulation test cell. Durian rind powder was prepared by cleaning and cutting the durian rind into small pieces of 1 to 2 cm, and then dried them in an oven at 60°C for 48 hours before grinding into five different sizes from coarse to ultra-fine while Hydro-plug, the commercial lost circulation material was supplied by Scomi Energy. The fluid loss test was conducted using a standard low pressure filter press while the bridging test was carried out at 100 psi of pressure difference and ambient temperature using a lost circulation cell. Fine durian in the water-based mud gave the best fluid loss control compared to coarse durian rind, fine and coarse Hydro-plug. The experimental results also showed that at 15 lb/bbl (42.8 kg/m3) optimum concentration, coarse and intermediate durian rind have outperformed Hydro-plug by showing an excellent control of mud losses in 1 and 2 mm simulated fractures
Z3-graded Grassmann Variables, Parafermions and their Coherent States
A relation between the -graded Grassmann variables and parafermions is
established. Coherent states are constructed as a direct consequence of such a
relationship. We also give the analog of the Bargmann-Fock representation in
terms of these Grassmann variables.Comment: 8 page
Generalized exclusion and Hopf algebras
We propose a generalized oscillator algebra at the roots of unity with
generalized exclusion and we investigate the braided Hopf structure. We find
that there are two solutions: these are the generalized exclusions of the
bosonic and fermionic types. We also discuss the covariance properties of these
oscillatorsComment: 10 pages, to appear in J. Phys.
On the construction of generalized Grassmann representatives of state vectors
Generalized -graded Grassmann variables are used to label coherent
states related to the nilpotent representation of the q-oscillator of
Biedenharn and Macfarlane when the deformation parameter is a root of unity.
These states are then used to construct generalized Grassmann representatives
of state vectors.Comment: 8 page
On the bicrossproduct structures for the family of algebras
It is shown that the family of deformed algebras has a different bicrossproduct
structure for each in analogy to the undeformed case.Comment: Latex2e file. 14 page
Twisted Rindler space-times
The (linearized) noncommutative Rindler space-times associated with
canonical, Lie-algebraic and quadratic twist-deformed Minkowski spaces are
provided. The corresponding deformed Hawking spectra detected by Rindler
observers are derived as well.Comment: 13 pages, no figures, keywords: quantum space-times, Hawking
radiatio
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