9,331 research outputs found
LDPC Codes for the Gaussian Wiretap Channel
No full textThis paper presents a coding scheme for the Gaussian wiretap channel based on low-density parity-check (LDPC) codes. The messages are transmitted over punctured bits to hide data from eavesdroppers. The proposed coding scheme is asymptotically effective in the sense that it yields a bit-error rate (BER) very close to 0.5 for an eavesdropper whose signal-to-noise ratio (SNR) is lower than the threshold SNR, even if the eavesdropper has the ability to use a bitwisemaximuma posteriori (MAP) decoder. Such codes also achieve high reliability for the friendly parties provided they have an SNR above a second threshold SNR. It is shown how asymptotically optimized LDPC codes are designed with differential evolution where the goal is to achieve high reliability between friendly parties while keeping the security gap SNR SNR as small as possible to protect against passive eavesdroppers. The proposed coding scheme is encodable in linear time, applicable at finite block lengths, and can be combined with existing cryptographic schemes to deliver improved data security by taking advantage of the stochastic nature of many communication channels
Asp-99 donates a hydrogen bond not to tyr-14 but to the steroid directly in the catalytic mechanism of Delta(5)-3-ketosteroid isomerase from Pseudomonas putida biotype B
No full textDelta(5)-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Delta(5)-3-ketosteroids at a rate approaching the diffusion Limit by an intramolecular transfer of a proton. Despite the extensive studies on the catalytic mechanism, it still remains controversial whether the catalytic residue Asp-99 donates a hydrogen bond to the steroid or to Tyr-14. To clarify the role of Asp-99 in the catalysis, two single mutants of D99E and D99L and three double mutants of Y14F/D99E, Y14F/D99N, and Y14F/D99L have been prepared by site-directed mutagenesis, The D99E mutant whose side chain at position 99 is longer by an additional methylene group exhibits nearly the same k(cat) as the wild-type while the D99L mutant exhibits ca. 125-fold lower k(cat) than that of the wild-type. The mutations made at positions 14 and 99 exert synergistic or partially additive effect on k(cat) in the double mutants, which is inconsistent with the mechanism based on the hydrogen-bonded catalytic diad, Asp-99 COOH...Tyr-14 OH ... C3-O of the steroid. The crystal structure of D99E/D38N complexed with equilenin, an intermediate analogue, at 1.9 Angstrom resolution reveals that the distance between Tyr-14 O eta and Glu-99 O epsilon is Ca. 4.2 Angstrom, which is beyond the range for a hydrogen bond, and that the distance between Glu-99 O epsilon and C3-O of the steroid is maintained to be ca, 2.4 Angstrom, short enough for a hydrogen bond to be formed. Taken together, these results strongly support the idea that Asp-99 contributes to the catalysis by donating a hydrogen bond directly to the intermediate
Ability of Anopheles gambiae mosquitoes to transmit malaria during the dry and wet season in an area of irrigated rice cultivation in The Gambia.
No full textThe seasonality of malaria transmission was studied in a Gambian village situated in an area where rice was cultivated. Observations were made during two dry seasons, when pump-fed irrigation was used to grow rice, and in the intervening rainy season, when rice was cultivated using a combination of irrigated and rain-fed paddies. Clinical episodes of malaria were mainly confined to the months during and soon after the rainy season. In the wet season the prevalence of parasitaemia was higher in febrile subjects than in afebrile controls but the reverse applied during the dry seasons. However, the biting rates of Anopheles gambiae complex mosquitoes in the two dry seasons (2.5 and 0.8 bites/child/night respectively) were greater than or similar to that in the rainy season (0.6 bites/child/night). The proportion of human bloodmeals (0.53 vs 0.75) and the survival of mosquitoes (parity rates of 0.41 vs 0.58) were both lower in the dry seasons than in the rains. The low prevalence of morbidity due to malaria in the dry season and the observed fall in the sporozoite rate may therefore have been due to a reduction in the vectorial capacity of the An. gambiae population. However, reduced transmission in the dry season may also have been due to the direct effect of high temperatures on the parasite in the vector
G2 & G1 plants species of SW Colorado
No full textPresented at the 16th symposium held on September 27, 2019 in Grand Junction, Colorado.2019 G2 species of SW Colorado -- 2019 G1 species of SW Colorado
Passively assembled optical inter-connection system based on an optical printed-circuit board
No full textWe propose a passively assembled chip-to-chip optical interconnection system using fiber-optic technology. To demonstrate the system, three components were prepared: a fiber-embedded optical printed-circuit board (OPCB), optical transmitter/receiver modules, and 90 degrees-bent fiber connectors. All components were assembled using precise guide pins and holes so that complete passive alignment was achieved in the OPCB. An optical link of 5-Gb/s/ch signals with a total link loss of -1.5 dB has been successfully demonstrated from the assembled system
Biochemical Characterization of the Transgenic Mouse Deficient of Inositol 1,4,5-triphosphate 3-kinase
No full textPCB-compatible optical interconnection using 45 degrees-ended connection rods and via-holed waveguides
No full textIn this paper, a new architecture for a chip-to-chip optical interconnection system is demonstrated that can be applied in a waveguide-embedded optical printed circuit board (PCB). The experiment used 45degrees-ended optical connection rods as a medium to guide light paths perpendicularly between vertical-cavity surface-emitting lasers (VCSELs), or photodiodes (PDs) and a waveguide. A polymer film of multimode waveguides with cores of 100 x 65 mum was sandwiched between conventional PCBs. Via holes were made with a diameter of about 140 mum by CO2-laser drilling through the PCB and the waveguide. Optical connection rods were made of a multimode silica fiber ribbon segment with a core diameter of 62.5 and 100 mum. One end of the fiber segment was cut 45degrees and the other end 90degrees by a mechanical polishing method. These fiber rods were inserted into the via holes formed in the PCB, adjusting the insertion depth to locate the 45degrees end of rods near the waveguide cores. From this interconnection system, a total coupling efficiency of about -8 dB was achieved between VCSELs and PDs through connection rods and a 2.5 Gb/s x 12-ch data link demonstrated through waveguides with a channel pitch of 250 mum in the optical PCB
Experimental demonstration of 10 Gbit/s transmission with an optical backplane system using optical slots
No full textA practical optical backplane system was prepared with transmitter-receiver processing boards and an optical backplane made from polymeric-waveguide-embedded optical printed-circuit boards. Optical slots were used as connection components between the transmitter-receiver processing boards and the backplane board to permit easy and repeatable insertion and extraction of the boards with micrometer precision. We report 10 Gbit/s data transmission between an optical backplane and the transmitter-receiver processing boards. (c) 2005 Optical Society of America
Role of the Three Cysteines in the Catalysis and Stability of Ketosteroid Isomerase from Psedomonas Putida Biotype B
No full textHigh-resolution crystal structures of Delta(5)-3-ketosteroid isomerase with and without a reaction intermediate analogue
No full textBacterial Delta(5)-3-ketosteroid isomerase (KSI) catalyzes a stereospecific isomerization of steroid substrates at an extremely fast rate, overcoming a large disparity of pK(a) values between a catalytic residue and its target. The crystal structures of KSI from Pseudomonas putida and of the enzyme in complex with equilenin, an analogue of the reaction intermediate, have been determined at 1.9 and 2.5 Angstrom resolution, respectively. The structures reveal that the side chains of Tyr(14) and Asp(99) (a newly identified catalytic residue) form hydrogen bonds directly with the oxyanion of the bound inhibitor in a completely apolar milieu of the active site. No water molecule is found at the active site, and the access of bulk solvent is blocked by a layer of apolar residues. Asp(99) is surrounded by six apolar residues, and consequently, its pK(a) appears to be elevated as high as 9.5 to be consistent with early studies. No interaction was found between the bound inhibitor and the residue 101 (phenylalanine in Pseudomonas testosteroni and methionine in P. putida KSI) which was suggested to contribute significantly to the rate enhancement based on mutational analysis. This observation excludes the residue 101 as a potential catalytic residue and requires that the rate enhancement should be explained solely by Tyr(14) and Asp(99). Kinetic analyses of Y14F and D99L mutant enzymes demonstrate that Tyr(14) contributes much more significantly to the rate enhancement Previous studies and the structural analysis strongly suggest that the low-barrier hydrogen bond of Tyr(14) (>7.1 kcal/mol), along with a moderate strength hydrogen bond of Asp(99) (similar to 4 kcal/mol), accounts for the required energy of 11 kcal/mol for the transition-state stabilization
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