Antipodal Configuration Research Articles

Ultra‐wideband fluidically steered antipodal Vivaldi antenna array

AbstractAn ultra‐wideband 1 × 4 antipodal Vivaldi antenna array with microfluidic beam steering is reported. The antipodal configuration is selected for its microstrip feed line, which is convenient for implementation of the phase‐shifting structure. Each antenna element uses a true‐time‐delay phase shifter consisting of nine microfluidic channels under its feed line in which deionized (DI) water, ɛ r = 77 + j13 (tanδ = 0.17) at 3 GHz, is pumped to change the speed of the propagating wave. The array was fabricated using a 1.52 mm thick substrate with ɛ r = 3.55 and tanδ = 0.0027. Each antenna element and phase shifter measures 55 mm × 140 mm. Measurements show that the array yields up to 90° of beam steering from 3 to 6.5 GHz and up to 40° of steering from 6.5 to 10 GHz. The array has a maximum realized gain of 13.1 dBi, and a half‐power beamwidth of less than 40° for all configurations.

A suite of neutron time-of-flight detectors to measure hot-spot motion in direct-drive inertial confinement fusion experiments on OMEGA

A suite of six neutron time of flight detectors capable of measuring the primary DT neutron energy spectrum has recently been completed on the OMEGA Laser System. The detectors are positioned along multiple quasi-orthogonal lines of sight (LOS’s) in either a stand-alone, collinear, or antipodal configuration. The collinear detector configuration enables one to measure the neutron velocity along the detector LOS independent of the neutron-production history, while the antipodal detector configuration enables one to directly measure of the hot-spot velocity along the detector axis and Gamow velocity shift due to the plasma ion temperature. Using these six measurements of the primary DT neutron energy spectrum, the neutron-averaged hot-spot velocity and Gamow velocity shift of DT fusion neutrons have been measured in cryogenic experiments on OMEGA for the first time. The detector suite is operable between DT neutron yields of 1 × 1013 to 2 × 1014 with an uncertainty of ∼14 km/s in the neutron-averaged hot-spot velocity measurement.

Planar, Compact Dual-Band Antenna for Wireless LAN Applications

A compact, printed dual-band antenna for WLAN applications is proposed. The radiating elements consist of a combination of a printed dipole for the lower resonant frequency and a bow-tie antenna for the upper resonant frequency. The operation on two separate bands is guaranteed by the use of two surface-mounted-device inductors. The antenna has been manufactured in antipodal configuration. Measurement results show good omnidirectionality and low cross-polarization levels.

(+)-Zwittermicin A: assignment of its complete configuration by total synthesis of the enantiomer and implication of D-serine in its biosynthesis.

(+)-Zwittermicin A: assignment of its complete configuration by total synthesis of the enantiomer and implication of D-serine in its biosynthesis.

Enantioselective synthesis of (-)-terpestacin and (-)-fusaproliferin: clarification of optical rotational measurements and absolute configurational assignments establishes a homochiral structural series.

An enantioselective synthesis of the syncytium formation inhibitor (-)-terpestacin (1, 19 steps, 5.8% yield from the allylation product of (R,R)-pseudoephedrine propionamide, 3) and the fungal metabolite (-)-fusaproliferin (2, 21 steps, 5.3% yield from 3) in their natural configurations is described. The route employs a series of stereoselective enolate alkylation reactions to establish the initial stereogenic center, set the quaternary carbon configuration, close the 15-membered ring, and introduce the side-chain residue with proper stereocontrol. Careful analysis of our synthetic materials alongside natural samples has revealed that several errors were made in the earlier measurements of optical rotation or in the absolute stereochemical assignments of these natural products. Clarifying all discrepancies, we show here that natural terpestacin (1) is levorotatory, not dextrorotatory as originally described, but was correctly assigned as the (1S,11S,15R,23S)-enantiomer. Fusaproliferin (2) is levorotatory, as reported, but is in fact the (1S,11S,15R,23S)-enantiomer and not the antipodal configuration originally assigned.

Impedance, attenuation and power-handling characteristics of double L-septa waveguides

Rectangular waveguides with two L-shaped septa attached to the broad walls in antipodal configuration have been shown theoretically by the authors (see ibid. vol.40, no.4, p.777-781, 1992) to be an improved variant of the double T-septa guide having larger cut-off wavelength and broader bandwidth of the dominant TE mode. Numerical data on the attenuation, impedance, and power handling capability of this new type of broadband guide are presented as additional design information.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An asymmetric synthesis of synthetic intermediates to thienamycin and epithienamycins A and B

An asymmetric synthesis for the synthetic intermediates to carbapenem antibiotics was examined via isoxazoline derivatives prepared by 1,3-dipolar cycloaddition between the nitrile oxide and menthyl crotonate. The (4S)-trans-azetidinone (14) having the antipodal configuration of thienamycin was synthesised in 16–20% e.e., while 85.3% e.e. of the (4R)-cis-azetidinone, possessing the same absolute configuration of epithienamycins A and B, was obtained by the same reaction procedure. The c.d. assignment of 3,4-dialkylated β-lactams is also described.

Signal Design for the Amplitude-Limited Gaussian Channel by Error Bound Optimization

A necessary and sufficient condition is presented for an input signal alphabet to optimize the random coding exponent for a time-discrete channel with signals restricted in amplitude. It is applied to the white noise Gaussian channel for signals in one and two dimensions. By use of this theorem the best input signal quantizafion is determined by numerical optimization. Results are presented on the number of amplitude or envelope levels needed to maximize the error bound parameter R 0 at different signal-to-noise ratios. For one-dimensional (baseband) signals a binary antipodal configuration is optimum, in the sense of maximizing R 0 , for signal-to-noise ratios below 6.9 dB. For two-dimensional (passband) signals with limited envelope, phase modulation is shown to be optimum for signal-to-noise ratios below 7.35 dB.

Absolute Configuration by X-ray and Circular Dichroism Methods of Calycanthine

THE absolute configurations of both (+)-2,5-dimethoxy-7-dimethylaminotriptycene1,2 and (−)-1,5-diamino-9,10-dihydro-9,10-ethenoanthracene3, as determined by the X-ray technique of Bijvoet4,5, are antipodal to the absolute configurations obtained from the circular dichroism (CD) spectra by application of molecular exciton theory, as developed by Mason6. From the similar CD spectra of related (+)-2,7-disubstituted triptycenes7 and (−)-1,5-disubstituted 9,10-dihydro-9,10-etheno- or -ethano-anthracenes3, Tanaka and colleagues have concluded that the contradiction is general. If that is the case and the two techniques have been correctly applied, then the theoretical basis of one or the other is unsound. Tanaka et al.7 accept the molecular exciton theory considerations and conclude that “the present method of determining the absolute configuration by the X-ray analysis should be changed so as to give the antipodal configuration”. This is an assertion that all absolute configurations determined by the Bijvoet technique are, and will be, wrong.

The theory of the optical activity and the absolute configuration of substituted triptycenes

Abstract The exciton theoretical analysis of the circular dichroism of the optically active triptycene derivatives is carried out and the absolute configuration is deduced from intensive spectral studies. The complicated CD spectra can be reasonably explained by the exciton interactions of the component chromophores. The foundation of the CD spectral analysis of the absolute configuration is explained in detail, and the absolute configurations are determined as 1 S 6 R for (+)-2-5-dimethoxy-7-substituted triptycenes. The configuration is not in agreement with that determined by the Bijvoet method of X-ray crystal analysis, but is in harmony with our proposal that the current method of X-ray analysis should be corrected so as to give the antipodal configuration.

Studies on the alkaloids of Securinega virosa Pax. et Hoffm.—I : Structure of virosecurinine

Investigation of Formosan Securinega visora Pax. et Hoffm. of the Euphorbiaceae family has led to the isolation of a new alkaloid named virosecurinine. The structure elucidation of this alkaloid (I) is described. Direct comparison of this alkaloid with securinine isolated from S. suffruticosa Rehd. reveals that securinine has the antipodal configuration of virosecurinine.