bluuebunny/crossref_metadata_2025 huggingface dataset:
Coding for the gaussian channel: The promise of weighted‐output decoding
Authors: Battail Gérard
Published: July 2007

We introduce the concept of weighted‐output decoding, which enables us to perform many successive decodings without information loss. The design of a coding system for the additive white Gaussian channel can thus be viewed as a means for combining many simple codes. We illustrate this concept by the example of parity‐check codes which are combined according to Elias' iterated product. Examination of the performance thus obtained leads us to criticize the conventional minimal distance criterion and to propose as a criterion a proximity measure of the weight distribution of the code with respect to the binomial one. According to this point of view, the iterated product of parity‐check codes appears as a means of decimation of the set of n‐tuples.
Low complexity concatenated coding schemes for digital satellite communications
Authors: Brine A. , Farrell P. G. , Harris R. A.
Published: July 2007

A study of reduced complexity concatenated coding schemes, for commercial digital satellite systems with low‐cost earth terminals, is reported. The study explored trade‐offs between coding gain, overall rate and decoder complexity, and compared concatenated schemes with single codes. It concentrated on short block and constraint length inner codes, with soft decision decoding, concatenated with a range of Reed‐Solomon outer codes. The dimension of the inner code was matched to the outer code symbol size, and appropriate interleaving between the inner and outer codes was used. Very useful coding gains were achieved with relatively high‐rate, low‐complexity schemes. For example, concatenating the soft decision decoded (9,8) single parity check inner code with the CCSDS recommended standard Reed‐Solomon outer code gives a coding gain of 4.8dB at a bit error probability of 10−5, with an overall rate of 0‐78.
Saw‐based chirp fourier transform and its application to analogue on‐board signal processing
Authors: Bakken Petter M. , Rønnekleiv Arne
Published: July 2007

This paper reports on the work done at ELAB‐RUNIT on surface acoustic wave (SAW) on‐board signal processing. The main processing is done by the analogue chirp Fourier transformer (CFT) and its inverse (ICFT). In a CFT, the input signal is transformed from an FDMA format to a TDM format and at the same time filtered by a filter bank. By multiplying and convolving the signal with chirp waveforms, the CFT is implemented by one bandpass cover filter and one chirp filter. The paper demonstrates that SAW reflector array compressors (RAC) built by ELAB‐RUNIT have suitable chirp responses and adequate precision for digital satellite communication. Two applications are described. An on‐board multicarrier demodulator (MCD) for 9·6 kb/s QPSK carriers and a processor for filtering, routeing and beam steering (FROBE) for flexible transparent repeaters. For MCDs the use of SAW CFTs leads to a power consumption for demultiplexing and A/D conversion of 15 mW per carrier with room for improvements. For transparent paylods, the FROBE leads to more flexibility and narrower guardbands than can be obtained by other analogue processors.
On‐board frequency demultiplexing by magnetostatic wave technologies
Authors: de Santis Pietro V.
Published: July 2007

Possible magnetostatic wave (MSW) implementations of variable bandwidth variable centre frequency (VBVCF) on‐board demultiplexers are presented. Hybrid technologies using magnetic thin films in conjunction with gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC) are introduced. New areas of research to advance the state of the art in this field are identified.
Distance measures for viterbi decoding of coded and bandlimited 8PSK signals
Authors: Cheung S. W. , Clark A. P.
Published: July 2007

The paper studies a digital modem that transmits a convolutionally encoded eight‐phase‐shift keyed (CE8PSK) signal over a satellite channel and employs a near‐maximum‐likelihood decoder at the receiver. Several different earth‐stations are assumed to have simultaneous access to a given transponder in the satellite as an arrangement of frequency‐division multiple access. Adjacent channel interference (ACI) is neglected here. The high‐power amplifier (HPA) at the earth‐station transmitter and the satellite transponder are assumed to be linear. The channel distorts the data signal, through the bandlimiting introduced by the equipment filters, and it adds stationary white Gaussian noise to the data signal at the receiver input. The resulting noisy and distorted data signal is coherently demodulated. Four different bandwidths of the transmitted CE8PSK signal are considered, together with three different demodulation processes. The decoder uses the Viterbi algorithm, together with one of six different distance measures to determine the costs of the stored vectors (survivors).

The paper describes the various techniques involved in the modem, and presents the results of an extensive series of computer‐simulation tests to measure the performances of the system with all appropriate combinations of the signal bandwidth, demodulation process and distance measure. The results of the tests are then used to determine the preferred modem design.
Performance study of 16‐ary deqam modem for future satellite communication systems
Authors: Cheung S. W. , Aghvami A. H.
Published: July 2007

This paper investigates the effects of additive white Gaussian noise (AWGN), adjacent‐channel interference (ACI) and co‐channel interference (CCI) combined with flat fading on the performance of bandlimited 16‐ary differentially encoded quadrature amplitude modulation (16‐ary DEQAM) signalling transmitted through a non‐linear high‐power amplifier (HPA). It is assumed that the HPA exhibits both AM‐AM and AM–PM conversion distortions. This situation may be applied to the up‐link or down‐link of a regenerative satellite system where the HPA is the earth‐station travelling‐wave tube (TWT) or the on‐board TWTA, respectively. The signal‐to‐noise ratio (SNR) degradations at a specific bit error rate (BER) are evaluated by means of a series of computer simulation tests for various values of channel roll‐off factor α (channel bandwidth) and different degrees of output backoff (OBO) of the HPA in the presence of various combinations of the channel impairments. It is shown that by employing a baseband or RF predistortion technique for the HPA and selecting the best arrangement of channel roll‐off factor, OBO value of the HPA and channel spacing, a good performance can be achieved regarding the most efficient use of bandwidth together with a minimum SNR degradation due to the presence of channel impairments. Thus, the use of 16‐ary DEQAM for satellite communications is feasible in the near future.
Performance of a CE16QAM modem in a regenerative satellite system
Authors: Cheung S. W.
Published: July 2007

This paper studies a digital modem for use over a regenerative satellite link. The modem transmits a convolutionally encoded 16‐ary quadrature‐amplitude‐modulated (CE16QAM) signal. The convolutional code has a three‐bit constraint length and a coding rate of 3/4. The high power amplifier (HPA) on board the satellite transmitter and at each station may introduce non‐linear distortion into the CE16QAM signal, but only a single‐link transmission is considered. Several different earth‐stations are assumed to be used in an arrangement of frequency division multiple access. Thus adjacent‐channel interference (ACI) can be introduced into the signal by the signals that occupy the immediately adjacent frequency bands.

Extensive computer‐simulation tests have been carried out to determine the effects of bandlimiting, non‐linear distortion and ACI, on the tolerance to additive white Gaussian noise of the modem, using an equivalent baseband model of the transmission system. The results are used to select the preferred system arrangement. It has been shown that, with 4 dB output back‐off (OBO) in the HPA, a bandwidth efficiency of 2·4 b/s Hz can be achieved, with an improvement in perforamnce of 2·5 dB, relative to that of an ideal uncoded eight‐phase‐shift keyed (8PSK) signal, at a bit‐error rate of 10·4.
Selective reject ALOHA/FCFS: An advanced VSAT channel access protocol
Authors: Raychaudhuri D.
Published: July 2007

This paper proposes and evaluates selective reject (SREJ) ALOHA/FCFS, a highly efficient, flexible and robust multiaccess protocol for very small aperture terminal (VSAT) applications. SREJ‐ALOHA with locally synchronous FCFS retransmission scheduling is a ‘semi‐compatible’ enhancement of asynchronous SREJ‐ALOHA, which has earlier been shown to be an attractive satellite channel sharing protocol for low volume bursty terminals with variable length messages. The FCFS retransmission scheduling policy proposed here broadens the applicability of SREJ‐ALOHA by providing higher maximum throughput, particularly in the important source traffic scenario with bimodal message length distributions. Improved channel‐sharing efficiency and delay are achieved by exploiting time‐of‐arrival feedback naturally embedded in an unslotted SREJ‐ALOHA channel to develop an implicit time‐of‐arrival based (FCFS) ordering for conflict‐free, locally synchronous retransmission of most contending messages. An analytical procedure for evaluation of stability, throughput and delay for a general finite source, variable message length traffic model is described. The model is used to demonstrate that random access SREJ‐ALOHA/FCFS typically achieves a maximum throughput in the region of 0·4–0·45 along with excellent stability and delay properties. In addition, a natural extension of the protocol which supports implicit reservation for long messages is described and shown to offer a high maximum throughput (>0·6), comparable to that achieved by highly co‐ordinated slotted systems, for example mixed interactive/file‐transfer traffic scenarios.
A carrier‐phased satellite receiving array
Authors: Brennan P. V.
Published: July 2007

The carrier‐phased array—in which array phasing is derived from the incident modulated signal—is conceptually a very simple means of achieving automatic beam pointing in communications systems. The technique is particularly suitable for satellite reception applications, although careful consideration must be given in a practical design due to problems associated with the low signal levels derived from satellite broadcasts. In this paper, the basic principles of operation of such an array are described and the requirements of a practical system are addressed, resulting in the design and evaluation of an array system suitable for use with BPSK modulated signals from a communications satellite.
Simulation of an on‐board hierarchical multistage digital FDM demultiplexer for mobile scpc satellite communications
Authors: Eyssele Helmut , Göckler Heinz
Published: July 2007

This paper is focused on the finite‐precision time‐domain simulation of the hierarchical multistage method detailed in References 1 and 2 for demultiplexing of an FDM signal being composed ofL= 32 slot signals. This approach to FDM demultiplexing is based on the processing of complex signals by linear‐phase FIR filters, where at any stage of processing the respective signals are always oversampled by a factor of two.

The simulation results fully confirm the system performance predicted in Reference 1 by modelling the distortions (spectral foldover and quantization noise) inherent in the system: assuming an ideal FDM signal at the input port of the analogue anti‐aliasing bandpass filter in front of the analogue‐to‐digital converter, a minimum signal‐to‐distortion ratio (S/D) of 30 dB is achieved at allLoutput ports of the demultiplexer with {w,wF,wi} = {11,12,14}, as anticipated in Reference 1. The signal word lengthwapply to the A/D conversion,wFto requantization between the filter stages, andwito filter internal signal processing.
On the digital signal processor based programmable real‐time reed‐solomon coding‐decoding system
Authors: Zheng Ou Yang Jing , Yong Un Ze
Published: July 2007

A real‐time high‐speed Reed‐Solomon coding—decoding system has been built based on a low‐cost signal processor TMS 32010. By taking advantage of the TMS 320 16‐bit multiplier and barrel shifter, the evaluation of the sum‐of‐products expression over a prime field can be simplified. Decoding of a (256,228) code with powerful error correcting capability over GF(257) has been implemented in this system, and the information bit rate is at least twice that of the ISDN B‐channel basic rate.
A statistical model of FM‐TV spectra for satellite interference and distortion prediction
Authors: Böck A. M. , Carpenter D. C. , Gallois A. P.
Published: July 2007

The requirement for a model of FM‐TV spectra in the planning procedure of satellite communication systems is introduced. Based on long‐term measurements of live TV channels, statistical properties of video spectra are examined and probability distributions for the luminance and chrominance components are proposed.

The spectrum of the frequency‐modulated signal is then derived, and signal distortion due to bandlimiting is calculated. Adjacent and cochannel interference effects are also investigated, with example cases illustrating influences of subcarrier loading and energy dispersion.

The proposed model, which describes FM‐TV spectra in terms of random variables, makes it possible to examine relative effects of system parameters, and will, therefore, be of benefit in the planning of new satellite services.
The intelsat slant‐path radiowave propagation experiments in tropical regions
Authors: Allnutt J. E. , Rogers D. V.
Published: July 2007

The requirement for INTELSAT to operate world‐wide in a diverse range of climates has motivated a number of experiments within the INTELSAT R&D programme to identify and model propagation impairments. The effects of some propagation phenomena, such as depolarization, were anticipated. Others (e.g. ionospheric scintillation at gigahertz frequencies) were unexpected or exhibited unusual features (rain attenuation in tropical climates). This paper presents the background of the INTELSAT R&D propagation measurements, with special emphasis on those in tropical regions, and provides the principal results. Several ongoing experiments are also discussed.
Rainfall rate characteristics for microwave systems in tropical and equatorial areas
Authors: Moupfouma Fidele , Martin Louis , Spanjaard Nicolas , Hughes Kevin
Published: July 2007

The wave propagation at frequencies from about 10 GHz can suffer rain effects such as attenuation, scattering and depolarization. The magnitude of these effects depends on rain characteristics. This paper presents results of the propagation experiments undertaken in Douala (Cameroon) and in Brazzaville (Congo) under the auspices of the ITU (Geneva) with the collaboration of CNET (France Telecom). Data based on five months measurements of rain rates in Douala with a network of four rain‐gauges are presented with reference also to some results of a propagation campaign in Brazzaville. The rain measurement period in Douala includes all of the rainy season. The measurement data are used to investigate the rain effect characteristics of the low latitude tropical regions of Africa and are discussed in relation to the influence of rain on microwave system performances in the region.
Some aspects of tropical rainfall and their effect on microwave propagation
Authors: Ajayi G. Olalere
Published: July 2007

Some characteristics of tropical rain rate and raindrop size distribution are briefly reported, making use of the data obtained at locations in Nigeria. Models and empirical relations have been obtained for the computation of the effects of tropical rain on radiowave propagation at centimetre and millimetre waves. Results are presented for the effect of integration time on rain rate as well as the rain‐rate duration characteristics, rain‐induced phase shift, attenuation and depolarization, in addition to the relationship between the rain rate and other rainfall parameters. Comparisons have also been made in many cases with the CCIR reports and results from other locations.
Elevation angle dependence in tropical regions
Authors: Bowthorpe B. J. , Andrews F. B. , Kikkert C. J. , Arlett P. L.
Published: July 2007

The variation of path attenuation with elevation angle has been generally considered to approximate a cosecant law, certainly between elevation angles of about 10° and 50°. Such a theory relies on the assumption that the attenuation layer is statiform for most of the time, and is therefore probably reasonable for temperate regions. In tropical areas however the incidence of convective rain is much higher than in temperate regions, so that during rainy periods, particularly at times of high rain rate, the assumption that the attenuating layer is stratiform is no longer valid. The cosecant law does not therefore hold in such conditions.

An experiment has been carried out in the tropical rain belt of northern Australia over several years to investigate the elevation‐angle dependency. Four radiometers were co‐sited, with the same azimuth. Three of these, with a half power beamwidth of 2.2°. were elevated to 15°, 45° and 85°. The fourth. with a beamwidth of 0·6° was elevated to 45° so as to allow an investigation into aperture effects. The antennae were all orientated for horizontal polarization. Rain‐gauges were co‐sited with the radiometers and placed along the look path.

The results obtained clearly indicate that, in tropical regions. the cosecant law is inappropriate for predicting the elevation angle effects of path attenuation. particularly at high rain rates. The presence of rain cells with rates exceeding 300 mm/h ensures that the assumption of a stratiform attenuating layer is invalid.
Measurements of 11 GHz attenuation using the intelsat V beacon in Indonesia
Authors: Juy M. , Maurel R. , Rooryck M. , Nugroho I. A. , Hariman T.
Published: July 2007

A campaign of measurements in Indonesia has been carried out according to a co‐operation agreement concluded between the Indonesian and French Administrations with the aim of estimating rain attenuation on slant paths. The experiment was planned using two earth‐stations, at Cibinong and Padang, both receiving a Ku‐band beacon from an INTELSAT V satellite, coupled with rain‐rate measurements at a number of sites.

Rain‐rate statistics are given for several locations in the Indonesian Archipelago. Cumulative distributions of attenuation and simultaneous rain rate, obtained at the earth‐stations, are presented. The analysis of the results has led to the proposal of an adaptation of the CCIR attenuation prediction method for low latitudes.
Conceptual design of rain radar for the tropical rainfall measuring mission
Authors: Nakamura Kenji , Okamoto Ken'Ichi , Ihara Toshio , Awaka Jun , Kozu Toshiaki , Manabe Takeshi
Published: July 2007

Specifications for a spaceborne rain radar for tropical rainfall measurement are described. A spaceborne rain radar has problems peculiar to rain observation from space. The radar must have a fast scanning mechanism to cover a large swath. Very weak rain echoes compared to the sea or land surface signal must be detected. These capabilities must be attained under the severe power consumption and mass limitations of the satellite bus.

The fast scanning requirement forces application of an electrically scanning mechanism. This requirement also causes a severe limitation of the available number of independent samples. The requirement for weak rain echoes excludes application of the pulse compression technique, which is a very conventional technique for other active microwave sensors on board satellites.

Under these constraints, a rain radar with an electrically scanning planar antenna at 13‐8 GHz is proposed.
Doppler‐shift correction by the DFT, for a QPSK satellite modem
Authors: Clark A. P. , Aftelak A. , Savjani M. , Ang C.
Published: July 2007

This paper describes a novel technique for the measurement and correction of the Doppler shift (frequency offset) in a received QPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non‐geostationary orbit, and correction of the Doppler shift is required to be achieved as soon as the satellite rises above the horizon, when the Doppler shift may be very high and the signal/noise ratio very low. The receiver now has no prior knowledge of the transmitted data, so that a non‐data‐aided system must be used, capable of operating under seriously adverse conditions.

The selected technique measures the DFTs of successive blocks of samples of the received and demodulated signal, and from the DFTs it derives a control signal for the VCO, which generates the in‐phase and quadrature reference carriers for the coherent demodulator. The frequency of the latter is adjusted to reduce the residual Doppler shift in the demodulated signal to a sufficiently small value, so that correct phase synchronization of the VCO on to the received signal carrier can then be achieved by means of an appropriate conventional system (not considered here).

The paper describes the new technique of Doppler shift correction, and presents the results of computer‐simulation tests to measure the time taken to correct an initial Doppler shift of 5 kHz in the received QPSK signal, at very low signal/noise ratios.
Analysis of random multiple access transmission systems
Authors: Phinainitisart N. , Wu William W.
Published: July 2007

For a very large number of small earth‐stations with varying transmission time and light traffic, the random multiple access (RMA) transmission system is capable of providing simultaneous access to earth‐stations by associating each station with a unique sequence of code symbols. Each information bit will be transformed into these code symbols, where each symbol is an entry in a discrete time‐frequency matrix. In this paper we propose a system model for RMA transmission systems and illustrate the application of RMA code sequences. The analysis of this transmission system, which causes interference to the desired signal, is presented. The performance parameter considered is the signal‐to‐noise ratio (SNR) at the output of a correlation detector. The analysis shows that the SNR depends on the number of users, the energy per data bit and the design of the time‐frequency matrix which determines the total numbers and values of the time‐delay units associated with any carrier.
CCITT/ANSI voice packetization protocol
Authors: Sherif M. H. , Clark R. J. , Forcina G. P.
Published: July 2007

This paper introduces the packetized voice protocol G.PVNP/T1.PVP which is being standardized in both the CCITT and T1Y1. At layer 2, G.PVNP/T1.PVP extends the ISDN LAPD protocol to include packetized voice, thereby potentially allowing the integration of voice and data traffic. Layer 3 specifies procedures to deal with voice‐band data traffic and to handle channel‐associated signalling.
Wideband packet technology in the integrated access and cross‐connect system (IACS)
Authors: Sherif M. H. , Malaret‐Collazo A. D. , Gruensfelder M. C.
Published: July 2007

The integrated access and cross‐connect system (IACS) is an AT&T product based on the wideband packet technology. The IACS has two components: the integrated access terminal (IAT) and the integrated access controller (IAC). The IAC provides centralized control, operations and maintenance for a network of IATs. An IAT provides direct digital connectivity at 1·536 Mb/s or 2·048 Mb/s to customer terminals and to circuit‐ and packet‐switched networks. It integrates voice, voiceband data, facsimile traffic, digital data, signalling, image and network control into packets of common format. It allows networking in both the circuit and packet domains, offers bandwidth on demand, and achieves graceful degradation of voice quality during congestion.
The development of an open‐network digital circuit multiplication equipment system
Authors: Kihlström Lars‐Olof , Viklund Nils , Bridgewater David
Published: July 2007

This paper discusses the systematization effort undertaken to generate an equipment specification of an extremely detailed and new nature for DCMEs in accordance with the INTELSAT specification IESS‐501. The main areas of importance addressed are additional to what has already been defined within the IESS‐501. A discussion of important aspects when introducing DCME into actual network conditions is also contained and results based on simulations of performance under simulated network environments are included.
Payload design for a switchboard in the sky
Authors: Berner W. , Ortwein F.
Published: July 2007

The architecture of an experimental payload with on‐board processing capabilities is described. Since the system is proposed as an experimental one it operates with only four beams in the 20/30 GHz frequency band. Special emphasis is put on the design of the switch and its associated control. The switch operates in a synchronous circuit‐switching manner and provides a throughput of 131 Mb/s. To derive the requirements for the on‐board controller, a process model is established. This model shows that an implementation in a finite state machine will not give enough flexibility. Therefore a microprocessor system is proposed for the controller.
The search for optimized shaping filters suitable for vsat systems
Authors: Tomlinson M. , Stevens R. , Saunders D.
Published: July 2007

The satellite communications industry has seen the emergence of VSAT (very small aperture terminal) systems with the promise of high growth in the next decade. The system design of the VSAT ground station has generally followed traditional satellite communication system design, namely featuring data transmission using QPSK (quadrature phase shift keying) or BPSK (binary phase shift keying) and 50 per cent raised cosine shaping filters with quasilinear transmission. Transmitter power is strictly limited and is at a premium for the VSAT transmitter which usually consists of a non‐linear solid‐state power amplifier (SSPA). Consequently it is important to operate the SSPA so that the maximum power is obtained, which means that the SSPA should be operated close to its saturation point. In so doing considerable distortion can be introduced, which leads to intersymbol interference (ISI) in the receiver and an associated degradation in error rate. Although constant envelope BPSK or QPSK solves the intersymbol interference problem and enables operation at the saturating point of the SSPA, the sinx/x spectral shape has unacceptable sidelobe levels.

This paper gives results of a search for a pulse shaping filter characteristic that is bandlimited and yet has improved performance over the traditional root 50 per cent cosine roll‐off filter when used in a VSAT ground station with a SSPA. The performance improvement due to improved shaping filtering is maintained over a range of output levels of the SSPA.

Performance evaluation results using computer simulation are presented.
Satellite antenna depointing originating from attitude control and station keeping specifications
Authors: Bousquet Michel , Maral Gérard
Published: July 2007

The paper establishes practical formulae in order to determine the depointing angle for a geostationary satellite antenna. Both satellite attitude and station‐keeping errors are considered. The attitude control and station‐keeping specifications give the amplitude of the angular motion of the satellite about its centre of mass and the amplitude of the displacement of the satellite with respect to its nominal position, respectively. The effects of these angular motions and displacements on the aiming of the satellite antenna are analysed. A set of formulae is derived which permits the calculation of the overall satellite antenna depointing angle. These formulae can be used for the estimation of the satellite antenna gain loss or interference contribution at a given location on the Earth.
Adapted packet speech interpolation
Authors: Lacovara R. C. , Vaman D. R.
Published: July 2007

Adapted packet speech interpolation (APSI) is presented as an evolution of digital speech interpolation (DSI) techniques. The inherent overload penalties of DSI are mitigated by the use of an overload strategy which distributes the penalties uniformly across all active speech sources. A novel use of linear delta modulation (LDM) allows the system to re‐encode the input sources at various rates depending upon the total offered load to the system. The subjective performance of hardware is discussed. Two models of silence and talk‐spurt behaviour (called activity) of speech are presented: an analytic model for single speakers obtained by the application of renewal theory, and a simulation model obtained from the analytic model.
An introduction to the NASA Shuttle ground operations simulator (SGOS)
Authors: Cook R. P.
Published: July 2007

The Shuttle ground operations simulator (SGOS) simulation software introduced in this paper is used to train NASA ground controllers and to certify launch countdown readiness. The SGOS executive and its subsystems have been an integral component of the Shuttle Launch Safety Program for almost 30 years. It is usable (via a LAN) by over 2000 NASA employees at the Kennedy Space Center and 11 000 contractors. SGOS supports over 800 models comprised of several hundred thousand lines of code and over 1000 Model Control Procedures. Copyright © 2007 John Wiley & Sons, Ltd.
Flavor reversion in soybean oil. VI. Isolation and identification of reversion compounds in unhardened soybean oil
Authors: Stapf R. J. , Daubert B. F.
Published: July 2007

Two compounds possibly contributing to the reverted flavor in soybean oil have been isolated from the condensate obtained from the deodorization of soybean oils.

From physical and chemical data compiled, including absorption and hydrogenation studies, the structure of the 2,4‐dinitrophenylhydrazones have been shown to correspond closely with the 2–4‐dinitrophenylhydrazones of Δ2:4 and acetaldehyde.
Biochemical modification of fats by microorganisms: A preliminary survey
Authors: Koritala S. , Hesseltine C. W. , Pryde E. H. , Mounts T. L.
Published: July 2007

Over 100 different strains of bacteria, actinomycetes, fungi and yeasts were incubated at 28 C for five days in the presence of soybean oil. Some soybean oil was consumed by many microorganisms, and some was also hydrolyzed to free fatty acids.Aspergillus oryzae, two different strains ofAmylomyces rouxii andRhizopus oligosporus hydrolyzed the oil completely (95%). The fatty acids fromAspergillus flavus fermentation contained less linolenic acid than the original soybean oil. Lipase was found intra‐ and extracellularly when microorganisms were grown in the presence of soybean oil.
Determination of individual tocopherols by derivative spectrophotometry
Authors: Bukovits Gabriel J. , Lezerovich Alberto
Published: July 2007

The second order derivative UV spectra of α‐, β‐, γ‐ and σ‐tocopherols showed small differences that allowed development of a derivative spectrophotometric method for determining individual tocopherols in a mixture. The procedure consists of measuring the second derivative spectrum of the sample at four specified wavelengths and calculating each concentration by means of a method for multicomponent analysis that uses mixtures as standards. Vegetable oils and other fatty products usually require a previous clean‐up process (under study) in order to remove interfering substances.
Mechanistic considerations of polymorphic transformations of tristearin in the presence of emulsifiers
Authors: Aronhime J. Schlichter , Sarig Sara , Garti N.
Published: July 2007

Fat polymorphs influence the quality of some food and cosmetic products. Emulsifiers traditionally have been added in order to retard undesired polymorphic transformations. The present study is an attempt to understand the role of selected emulsifiers on such transformations. Tristearin was heated or aged under controlled conditions using differential scanning calorimetry (DSC) and X‐ray techniques, and the extent of transformation was evaluated in view of the possible pathways of α transforming into β. The temperature regime controls the extent of mobility of fat molecules, the local crystal imperfections and the degree of liquefaction. As a result, it dictates the kinetics of the polymorphic transformation.

The surfactant added as an impurity does not have a straightforward effect, as thought previously, but rather varies with the kinetic conditions. During aging some selected solid emulsifiers will retard the α‐β transformation while others still enhance it (during heating, all of them will inhibit β form crystallization). Their effect probably is related to different crystalline organizations and the creation of imperfections. Liquid emulsifiers in any case will enhance the α‐β transformation, due probably to their weak structure compatibility with tristearin, which causes a higher mobility of triglyceride molecules.
Characterization of peanut oil tricacyglycerols by HPLC, GLC and EIMS
Authors: Singleton J. A. , Pattee H. E.
Published: July 2007

Twenty‐three peanut oil triacylglycerols have been characterized by liquid chromatography, gas chromatography and electron impact mass spectrometry. High resolution was achieved using two 8‐cm × 6.2‐mm reverse phase columns in series, and 20 of the triacylglycerols were separated in an analysis time of less than 45 min. Triacylglycerols were identified by analyzing each liquid chromatography fraction for carbon number, fatty acid composition and mass fragmentation pattern. The combined application of these methods permitted the identification of triacylglycerols representing combinations of all of the fatty acids present in peanut oil.
Reverse-Flow Posterior Interosseous Flap—A Review of 68 Cases
Authors: Cheema Tahseen A. , Lakshman Shankar , Cheema Mohammad Amin , Durrani Shakeel Farrukh
Published: July 2007

We are reporting our 10-year experience with 68 patients. Sixty-six flaps were of fasciocutaneous type and two were of osteofasciocutaneous type. These flaps were used for volar and dorsal traumatic hand defects, first web space reconstruction, thumb reconstruction, and repair of congenital anomalies. Sixty flaps (88.24%) had complete uneventful take-up. Four flaps developed partial necrosis, whereas four flaps suffered complete necrosis. The single most important factor for flap survival in our experience has been inclusion of at least two perforators to supply the skin pedal. The proximal flap dissection has a learning curve and all of our poor results were in the early part of our experience. We believe that posterior interosseous fasciocutaneous flap (PIF) is a versatile and reliable option for the challenging problems of hand soft-tissue coverage.
Methodology for the In Vivo Measurement of the Δ9‐Desaturation of Myristic, Palmitic, and Stearic Acids in Lactating Dairy Cattle
Authors: Mosley Erin E. , McGuire Mark A.
Published: July 2007

There is limited methodology available to quantitatively assess the activity of the Δ9‐desaturase enzyme in vivo without chemically inhibiting the enzyme or using radioactively labeled substrates. The objective of these experiments was to develop methodology to determine the incorporation and desaturation of 13C‐labeled fatty acids into milk lipids. In a preliminary experiment, 3.7 g [1‐13C]myristic acid ([1‐13C]14:0), 19.5 g [1‐13C]palmitic acid ([1‐13C]16:0), 20.0 g [1‐13C]stearic acid ([1‐13C]18:0) were combined and infused into the duodenum of a cow over 24 h. In a following experiment, 5.0 g [1‐13C]14:0, 40.0 g [1‐13C]16:0, and 50.0 g [1‐13C]18:0 were infused into the abomasums of separate cows as a bolus over 20 min or continuously over 24 h. Milk fat was extracted using chloroform:methanol. Fatty acids were methylated, and fatty acid methyl esters (FAME) were converted to dimethyl disulfide derivatives (DMDS). The FAME and DMDS were analyzed by gas chromatography mass spectrometry. In the preliminary experiment, 13C enrichment in 14:0 but not 16:0 or 18:0 was observed. When dosage amounts were increased in the following experiment, peak enrichments from the bolus infusion were observed at 8 h. Enrichments for continuous infusion peaked at 16 h for 14:0 and 18:0, and at 24 h for 16:0. The Δ9‐desaturase products of these fatty acids were estimated to be 90% of cis‐9 14:1, 50% of cis‐9 16:1, and 59% of cis‐9 18:1. This study demonstrates that 13C‐labeled fatty acids may be utilized in vivo to measure the activity of the Δ9‐desaturase enzyme.
Continuous‐phase fat crystals strongly influence water‐in‐oil emulsion stability
Authors: Hodge S. M. , Rousseau D.
Published: July 2007

To elucidate the role of continuous‐phase fat crystals on emulsion destabilization, water‐in‐canola oil emulsions prepared with 0–2% (w/w) added solid fat (hydrogenated canola stearine or hydrogenated cottonseed stearine) were examined using pulsed NMR droplet‐size analysis, sedimentation, and microscopy. Droplet‐size analysis showed that addition of either fat prior to emulsification (precrystallized fat) or fat quench‐crystallized in situ following emulsification (postcrystallized fat) decreased the degree of droplet coalescence, based on volume‐weighted (d33) mean droplet diameters, with postcrystallized emulsions being more stable against coalescence. Sedimentation studies corroborated these results, with greatly enhanced stability against sedimentation in postcrystallized emulsions. Precrystallized fat had very little effect on emulsion sedimentation at levels as high as 2% (w/w). Postcrystallized cottonseed stearine produced slightly less resistant emulsions than did canola stearine, even if both were in the β‐form. Surface energetics revealed that canola stearine had greater affinity for the oil/water interface and hence a greater displacement energy. The presence of micronsized (Pickering) crystals located directly at the droplet interface, resulting from in situ crystallization or generated by the shearing of precrystallized fats, provided enhanced stability vis‐à‐vis preformed crystals. These stabilized emulsions via the formation of crystal networks that partially immobilized droplets.
Composition of phenolic acids in sea buckthorn (Hippophae rhamnoides L.) berries
Authors: Zadernowski R. , Naczk M. , Czaplicki S. , Rubinskiene M. , Szałkiewicz M.
Published: July 2007

The composition of phenolic acids in several varieties of sea buckthorn berries was determined by GC and MS. In six cultivars the total content of phenolic acids ranged from 3570±282 to 4439±405 mg per kg of berries, on a dry basis. Seventeen phenolic acids were tentatively identified in the berries. Salicylic acid was the principal phenolic acid in sea buckthorn berries, accounting for 55 to 74.3% of the total phenolic acids present. The phenolic acids liberated from esters and glycosidic bonds were the major fractions of phenolic acids in the berries, whereas free phenolic acids constituted only up to 2.3% of total phenolic acids present.
Synthesis of mycolic acid biosurfactants and their physical and surface‐active properties
Authors: Lee Myungjin , Gwak Hyung Sub , Park Byeong Deog , Lee Sung‐Taik
Published: July 2007

Five mycolic acids [2‐alkyl‐3‐hydroxy FA: R1C*(OH)C*HR2COOH] were synthesized using acyl chlorides with alkyl chains of different lengths (total carbon numbers of mycolic acids, 12, 16, 20, 24, 36). The relationship between the chemical structures of the mycolic acids and their surface‐active properties was determined. The acids were synthesized in three steps: (i) dimerization of acyl chloride into alkyl ketene dimer, (ii) selective reduction of C=C to C‐C by hydrogenation, and (iii) β‐lactone ring cleavage under alkaline conditions. The yields of C12‐, C16‐, C20‐, C24‐, and C36‐mycolic acid were 72, 73, 73, 73, and 73%, respectively. The critical micelle concentrations (CMC) of C12‐, C16‐, and C20‐mycolic acid were 2.2×10−4, 1.36×10−4, and 7.4×10−5 M, respectively. As the carbon number increased, the surface tension at the CMC value was also lower; the values for C12‐, C16‐ and C20‐mycolic acid were 46.54, 43.59, and 41.57 dyn/cm, respectively. The emulsifying activities of mycolic acids were determined for n‐tetradecane, n‐hexadecane, cyclohexane, and diesel oil. The results showed that C12‐mycolic acid was the best emulsifier for diesel oil, C16‐mycolic acid was the best emulsifier for n‐tetradecane and n‐hexadecane, and C20‐mycolic acid was the best emulsifier for cyclohexane. This study showed that mycolic acids having, surface‐active properties can be chemically synthesized for potential applications in the detergent/cleaning material industries, for example, in oil spill cleanup, oil recovery, textiles, pharmaceuticals, and cosmetics.
Free radical meleation of soybean oil via a single‐step process
Authors: Tran Phuong , Seybold Ken , Graiver Daniel , Narayan Ramani
Published: July 2007

In this study a new value‐added product was developed from soybean oil for use as a chemical feedstock. The investigation and optimization of this work resulted in a fast and simple process to maleate soybean oil. An anhydride functionality was introduced into soybean oil through a free radical‐initiated maleation. Two initiators were evaluated, 2,5‐bis(tert‐butylperoxy)2,5‐dimethylhexane peroxide and di‐tert‐butyl peroxide. The effects of reaction time, initiator concentration, maleic anhydride concentration, and reaction temperature were investigated. The maleated soybean oil was characterized using acid value, iodine value, and FTIR spectroscopy. The acid value was directly related to the initial concentration of maleic anhydride, whereas the concentration and type of initiator had little effect on the acid value. The peroxide‐initated functionalization of soybean oil with maleic anhydride in a closed vessel at elevated pressure and temperature was found to proceed by a Diels‐Alder mechanism.
A novel process for physically refining rice bran oil through simultaneous degumming and dewaxing
Authors: Rajam L. , Soban Kumar D. R. , Sundaresan A. , Arumughan C.
Published: July 2007

A new process for the physical refining of rice bran oil through combined degumming and dewaxing was developed on a laboratory scale and then demonstrated on a commercial scale. The simultaneous degumming and dewaxing of the crude oil with a solution of water and CaCl2, followed by crystallization at a low temperature (20°C), facilitated precipitation of the hydratable and nonhydratable phosphatides along with the wax, which enabled its separation and reduction to a greater extent. Bleaching and subsequent winterization (20°C) of this oil further reduced the phosphorus content to less than 5 ppm. Thus, these pretreatment steps enabled the physically refined rice bran oil to meet commercially acceptable levels for color, FFA content, and cloud point values (10–12 Lovibond units in a 1‐in, cell, <0.25%, and 4–5°C, respectively) with very low neutral oil loss; this has not been observed hitherto. Rice bran oil is known for its high levels of bioactive phytochemicals, such as oryzanol, tocols, and sterols. The process reported here could retain more than 80% of these micronutrients in the end product.
Functional invalidation of the autotaxin gene by a single amino acid mutation in mouse is lethal
Authors: Ferry Gilles , Giganti Adeline , Cogé Francis , Bertaux Fabien , Thiam Kader , Boutin Jean A.
Published: July 2007

Autotaxin is a member of the phosphodiesterase family of enzymes, (NPP2). It is an important secreted protein found in conditioned medium from adipocytes. It also has a putative role in the metastatic process. Based on these observation, further validation of this potential target was necessary, apart from the classical biochemical ones. The construction of a knock out mouse strain for ATX was started. In this paper, we report the generation of a mouse line displaying an inactivated ATX gene product. The KO line was designed in order to generate a functional inactivation of the protein. In this respect, the threonine residue T210 was replaced by an alanine (T210A) leading to a catalytically inactive enzyme. If the experimental work was straight forward, we disappointedly discovered at the final stage that the breeding of heterozygous animals, ATX −/+, led to the generation of a Mendelian repartition of wild‐type and heterozygous, but no homozygous were found, strongly suggesting that the ATX deletion is lethal at an early stage of the development. This was confirmed by statistical analysis. Although other reported the same lethality for attempted ATX−/− mice generation [van Meeteren, L.A., Ruurs, P., Stortelers, C., Bouwman, P., van Rooijen, M.A., Pradère, J.P., Pettit, T.R., Wakelam, M.J.O., Saulnier‐Blache, J.S., Mummery, C.L., Moolenar, W.H. and Jonkers, J. (2006) Autotaxin, a secreted lysophospholipase D, is essential for blood vessel formation during development, Mol. Cell. Biol. 26, 5015–5022; Tanaka, M., Okudaira, S., Kishi, Y., Ohkawa, R., Isei, S., Ota, M., Noji, S., Yatomi, Y., Aoki, J., and Arai, H. (2006) Autotaxin stabilizes blood vessels and is required for embryonic vasculature by producing lysophosphatidic acid, J. Biol. Chem. 281, 25822–25830], they used more drastic multiple exon deletions in the ATX gene, while we chose a single point mutation. To our knowledge, the present work is the first showing such a lethality in any gene after a point mutation in an enzyme catalytic site.
Response of the central metabolism of Escherichia coli to modified expression of the gene encoding the glucose‐6‐phosphate dehydrogenase
Authors: Nicolas Cécile , Kiefer Patrick , Letisse Fabien , Krömer Jens , Massou Stéphane , Soucaille Philippe , Wittmann Christoph , Lindley Nic D. , Portais Jean-Charles
Published: July 2007

The deletion of the zwf gene encoding G6PDH activity led to restructuring of the carbon flux through central metabolism in Escherichia coli, though over‐expression of this gene had only minor consequences for overall carbon flux. The modified carbon flux seen in the zwf deletion mutant enabled alternative routes of anabolic precursor formation and an adequate supply of NADPH synthesis via a modified TCA cycle to be generated so as to sustain growth rates comparable to the WT.
Disruption of the cortical actin cytoskeleton does not affect store operated Ca2+ channels in human T‐cells
Authors: Mueller Philipp , Quintana Ariel , Griesemer Desiree , Hoth Markus , Pieters Jean
Published: July 2007

Lymphocyte signaling and activation leads to the influx of extracellular Ca2+ via the activation of Ca2+ release activated Ca2+ (CRAC) channels in the plasma membrane. Activation of CRAC channels occurs following emptying of the endoplasmic reticulum intracellular Ca2+ stores. One model to explain the coupling of store‐emptying to CRAC activation is the secretion‐like conformational coupling model. This model proposes that store depletion increases junctions between the endoplasmic reticulum and the plasma membrane in a manner that could be regulated by the cortical actin cytoskeleton. Here, we show that stabilization or depolymerization of the actin cytoskeleton failed to affect CRAC activation. We therefore conclude that rearrangement of the actin cytoskeleton is dispensable for store‐operated Ca2+ entry in T‐cells.
Aggregation of Light‐Harvesting Complex II leads to formation of efficient excitation energy traps in monomeric and trimeric complexes
Authors: van Oort Bart , van Hoek Arie , Ruban Alexander V. , van Amerongen Herbert
Published: July 2007

Non‐photochemical quenching (NPQ) protects plants against photodamage by converting excess excitation energy into harmless heat. In vitro aggregation of the major light‐harvesting complex (LHCII) induces similar quenching, the molecular mechanism of which is frequently considered to be the same. However, a very basic question regarding the aggregation‐induced quenching has not been answered yet. Are excitation traps created upon aggregation, or do existing traps start quenching excitations more efficiently in aggregated LHCII where trimers are energetically coupled? Time‐resolved fluorescence experiments presented here demonstrate that aggregation creates traps in a significant number of LHCII trimers, which subsequently also quench excitations in connected LHCIIs.