End Station Research Articles

Distribution of solutes, microbes and invertebrates in river sediments along a riffle‐pool‐riffle sequence

Summary 1 Unlike riffles, research has focused rarely on the hyporheic zone of pools. To highlight the functioning of a pool, field investigations were performed in a riffle-pool-riffle sequence by integrating simultaneously physico-chemistry, microbes and invertebrates. The study was conducted in a channel characterised by strong downwelling of surface water. 2 To include the downstream flux of water within the sediment, a longitudinal profile was studied along six stations situated: at the centre (Station 1) and at the lower end (Station 2) of the first riffle, at the upstream part (Station 3), at the centre (Station 4, at the inflection point) and at the lower end (Station 5) of the pool, and at the centre of the second riffle (Station 6). At each station, three replicate samples were taken and three sample depths were investigated (0.2, 0.5, and 1.0 m below the stream bed) on two dates. 3 Physico-chemical parameters (vertical hydraulic gradient, oxygen concentration and specific conductance) differed between stations depending on infiltration rates. In contrast, organic matter and microbial parameters presented patchy distributions linked with factors other than the geomorphological pattern. Despite not very pronounced geomorphologic features, the slope variation at the centre of the pool (at the inflection point) affects the distribution of epigean and hypogean invertebrates. 4 Based upon faunal parameters, the pool could be divided into an upstream and a downstream part, the latter being more strongly influenced by surface water. 5 The pool should be considered as a heterogeneous area. In that respect, the inflection point of a pool may be as important as the top of a riffle in the functioning of river sediments.

Multiwavelength control protocols for WDM networks with restricted data channel collision

A new network architecture which uses several wavelengths as control channels for co-ordination of packet transmissions on data channels for single-hop WDMA networks and passive star topology is introduced in this paper. The presented multiwavelength control architecture distributes control information over the total control channels and in conjunction with a suitable network interface, reduces the headers electronic processing bottleneck at each end station. Also, the access schemes decrease the contention on data channels by avoiding part of the data channel collision. Some cases of multiple access protocols for asynchronous and synchronous (re)transmission categories are suggested. The proposed schemes adopt the slotted ALOHA protocol for the access to control and data multichannel systems in which the data packets transmission starts immediately after the control packets transmission. An analytic model is developed and analysed for performance measures evaluation based on Poisson approximations statistics and a finite population. The effect of receiver collision is analysed and estimated by the average rejection probability at destination. Also, numerical results are discussed for various numbers of control and data channels. Copyright © 2000 John Wiley & Sons, Ltd.

An autocompensating fiber-optic quantum cryptography system based on polarization splitting of light

We have developed a system for quantum key distribution (QKD), based on standard telecommunication lasers, detectors, and optical fiber, that passively compensates for time-dependent variations of the fiber-optic path due to stress, temperature changes, or birefringence. This approach allows information encoded in phase shifts imposed on single-photon-level pulses to be accurately read out after transmission over many kilometers of uncontrolled fiber. Cooled InGaAs avalanche photodiodes, pulse-biased using a special noise canceling circuit, are used to detect single 1.31-/spl mu/m infrared photons with a high efficiency, low dark-count rate, and subnanosecond time resolution. A single optical fiber carries both the quantum information and precise 1.55 /spl mu/m timing pulses between the two end stations. Overall synchronization of end-station activities, public discussion of basis choices, error correction, and privacy amplification have all been implemented over a local area network (LAN). The system at present generates raw, error-corrected, and privacy-amplified key data at rates of /spl sim/1000, 600, and 200 bits/s, respectively, over a 10-km single-mode fiber link.

The ATM Switch and Header Error Control FPGA Implementation

Design and implementation of recent advances in high-speed networking technology and the associated demand for flexibility have resulted in the emergence of Asynchronous Transfer Mode (ATM) as the ultimate solution for Broadband Integrated Services Digital Network (B-ISDN). An implementation ofATM network consists of user end stations that send and receive data cells over virtual connections. These connections are implemented by using a switching system. The switching system consists of a switch that routes the data cells and a line of each link or group of links. The ATM switch includes not only routing and cell processing, but takes on some other functions of control. The FPGA implementation is optimised for short time response and compact solution.

Connection splitting: an efficient way of reducing call blocking in ATM

In this paper, we propose a technique for reducing asynchronous transfer mode (ATM) call blocking which is achieved by splitting wide-band connections into multiple low-bandwidth subconnections and routing them independently through the network. The essence of the mechanism is to use fragmented network bandwidth for supporting calls which are otherwise blocked by conventional routing. ATM bandwidth fragmentation may take place in a situation when a connection occupies a part of a link bandwidth and the rest of it is not sufficient for another connection. The unused bandwidth becomes fragmented. We provide a detailed cell-level design for the split-scheduling algorithms, which use a special type of ATM resource management cell for maintaining cell ordering. The analysis and simulation of the scheduling algorithms show that connection splitting is capable of delivering acceptable cell-level quality of service to multiple traffic classes. We also deliver a solution for implementing splitting without requiring any protocol changes within the network. We show that it is sufficient to modify the data and control plane protocols only within the end stations. Finally, a set of routing-level simulations for splitting demonstrates that splitting can reduce blocking by up to 45% for high-bandwidth calls in a moderately loaded network. Considering that it does not incur any network expenses or protocol changes, we propose splitting as an efficient means for reducing connection blocking.

A transparent WDM network featuring shared virtual rings

We propose and demonstrate a transparent wavelength division multiplexing (WDM) metro ring architecture in which optics enables simultaneous provisioning of dedicated wavelengths for high-end users, while low-end users share wavelengths on virtual rings. All wavelengths are sourced by the network and remotely modulated at customer end stations (ES) by low-cost semiconductor optical amplifiers (SOAs), which also serve as transmission amplifiers. Measured bit error rate (BER) data for three different ring configurations show negligible power penalties associated with upstream transmission around a 120-km 3-mode ring through as many as four cascaded SOA/modulators. Preliminary tests indicate that the SOAs are suitable modulators for packet transmission over the network.

Spatial sensitivity of macaque inferior temporal neurons

Recent findings in dorsal visual stream areas and computational work raise the question whether neurons at the end station of the ventral visual stream can code for stimulus position. The authors provide the first detailed, quantitative data on the spatial sensitivity of neurons in the anterior part of the inferior temporal cortex (area TE) in awake, fixating monkeys. They observed a large variation in receptive field (RF) size (ranging from 2.8 degrees to 26 degrees ). TE neurons differed in their optimal position, with a bias toward the foveal position. Moreover, the RF profiles of most TE neurons could be fitted well with a two-dimensional Gaussian function. Most neurons had only one region of high sensitivity and showed a smooth decline in sensitivity toward more distal positions. In addition, the authors investigated some of the possible determinants of such spatial sensitivity. First, testing with low-pass filtered versions of the stimuli revealed that the general preference for the foveal position and the size of the RFs was not due simply to TE neurons receiving input with a lower spatial resolution at more eccentric positions. The foveal position was still preferred after intense low-pass filtering. Second, although an increase in stimulus size consistently broadened spatial sensitivity profiles, it did not change the qualitative features of these profiles. Moreover, size selectivity of TE neurons was generally position invariant. Overall, the results suggest that TE neurons can code for the position of stimuli in the central region of the visual field.

Characterizing the optimal allocation of storage space in production line systems with variable processing times

We consider the optimal allocation of buffer storage spaces in unpaced production lines with variable processing times. It is known that for a fixed total number of buffer spaces, the production rate can often be improved by deliberately unbalancing the buffer allocations in an inverted bowl pattern (the “storage bowl phenomenon”), with more storage space allocated to the internal stations than to the end stations. It has been hypothesized that if the total number of buffer spaces is also a decision variable, then for a reasonable cost model the optimal allocation would have one additional storage space at each of the internal stations. This paper uses a cost model to show that the optimal allocation is more complicated than this. For balanced lines, the inverted bowl pattern is typically optimal, but the bowl shape becomes more and more pronounced (in an absolute sense) with larger numbers of buffer spaces. However, the relative shape of the bowl stays fairly constant. However, if the workload is unbalanced, the buffer space pattern deviates from the bowl pattern by reducing the number of buffer spaces in buffers that are not adjacent to the bottleneck machine.

Characterizing the optimal allocation of storage space in production line systems with variable processing times

We consider the optimal allocation of buffer storage spaces in unpaced production lines with variable processing times. It is known that for a fixed total number of buffer spaces, the production rate can often be improved by deliberately unbalancing the buffer allocations in an inverted bowl pattern (the “storage bowl phenomenon”), with more storage space allocated to the internal stations than to the end stations. It has been hypothesized that if the total number of buffer spaces is also a decision variable, then for a reasonable cost model the optimal allocation would have one additional storage space at each of the internal stations. This paper uses a cost model to show that the optimal allocation is more complicated than this. For balanced lines, the inverted bowl pattern is typically optimal, but the bowl shape becomes more and more pronounced (in an absolute sense) with larger numbers of buffer spaces. However, the relative shape of the bowl stays fairly constant. However, if the workload is unbalanced, the buffer space pattern deviates from the bowl pattern by reducing the number of buffer spaces in buffers that are not adjacent to the bottleneck machine.

Waveguide spectral multiplexers/demultiplexers

Configurations, basic characteristics, and the methods for implementation of wavelength-division multiplexers/demultiplexers as the key elements of the end stations in fiber-optics eonnnunication systems axe considered. The most important studies directed at practical implementation of wavelength-division multiplexers in specific devices based on SiO,~ and InP are reviewed in detail. SiO2-based multiplexers exhibit lower losses, whereas devices based on InP make it possible to use the technologies of microelectronics and integrating optics and to fabricate radiation sources and passive components on the same substrate. Schemes for optical multiplexers with adding and dropping of channels and examples of their implementation are given. It is emphasized that high-density wavelength-division multiplexers have small sizes and are fabricated by conventional lithography, which makes them promising in wideband optical commmfieation systems.

Estimation de la qualité des eaux du Nahr Beyrouth. Utilisation de l'indice diatomique de polluo-sensible (IPS)

The quality of Nahr Beirut's water, supplying water to Beirut and the suburbs, has been studied. A complete algology and chemical study has been conducted. The diatoms are considered one of the best bioindicators of the water's surface because they react directly with organic pollutants and they need a very ecological medium. The use of some diatomic indicators and the polluo-sensible ones (IPS) is widespread in the French hydrographic network. The methodology applied in our biotope showed good results around the head-water and dramatic deterioration around Beirut city. Water samples were collected periodically and analyzed for HCO, Cl, and HNO, and for the major ions/Ca, Mg, Na and K, and for some trace elements. Atomic absorption spectrometry using flame acetylene was used to measure the alkaline metals, whereas graphite furnace was used for the determination of trace elements. It has been found that the major composition in rivers is predominantly influenced by the composition of parent rocks in Lebanon. The slightly elevated values of PH (7.7) in the rivers and the large amount of carbonate HCO, dolomite CaMg (CO) and limestone. These compounds lead to elevated concentration of Ca and Mg in the studied stations. The concentration of the major ions varied with the cationic dominance order of Ca > Mg > Na > K which is compatible with the common natural major ion assemblages established for world rivers. The concentration of the major ions are also predominantly influenced by the Chemical weathering of rocks and minerals. The mean concentration of nitrates increased in urban and agriculture areas. The mean concentration of trace elements in the freshwater increased with increasing distance from the headwater, particularly at Ain el Delbe and the end station of Jisr Bacha, a consequence of anthropogenic inputs. In fact the above mentioned stations are located in industrial and popular areas. (author)

A multiwavelength control architecture for electronic processing bottleneck reduction in WDMA lightwave networks

In this paper we propose a new network architecture which uses several wavelengths as control channels for coordination of packet transmissions on data channels for single-hop WDMA networks and passive star topology. The distribution of control information over a number of control channels in conjunction with a suitable network interface reduces the electronic processing bottleneck at one of the end stations. Time is divided into fixed size cycles. The proposed schemes adopt the slotted ALOHA protocol for the access to control and data multichannel systems and differ in the adopted policy for data packet transmission. Analytic model is developed and analyzed for performance measures evaluation based on Poisson approximation statistics of both the infinite and finite population. Numerical results are discussed for various numbers of control and data channels. The effect of receiver collisions is analyzed and estimated by the average rejection probabilities at destination. Also simulation results are presented for comparison with the results obtained by performance analysis.

The Seat Reservation Problem

We investigate the problem of giving seat reservations on-line. We assume that a train travels from a start station to an end station, stopping at $k$ stations, including the first and last. Passengers may attempt to make reservations at any point before they get on the train. Reservations can be made going from any station to any later station. The train has a fixed number of seats. The seat reservation system attempts to maximize income. We consider the case in which all tickets cost the same amount and the case in which the cost of a ticket is proportional to the length of the trip. In these cases, we prove upper and lower bounds of $\Theta(1/k)$ on the competitive ratio of any ``fair'''' deterministic algorithm. We also define the ``accommodating ratio'''' which is similar to the competitive ratio except that the only sequences of requests allowed are sequences for which the optimal off-line algorithm could accommodate all requests. We prove upper and lower bounds of $\Theta(1)$ on the accommodating ratio of any ``fair'''' deterministic algorithm, in the case in which all tickets have the same cost, but $\Theta(1/k)$ in the case in which the ticket cost is proportional to the length of the trip. The most surprising of these results is that all fair algorithms are at least $1/2$-accommodating when all tickets have the same cost. We also consider concrete algorithms; more specifically, First-Fit and Best-Fit.

Measurement of the nucleon g2 spin structure function at SLAC

The deep inelastic polarized structure functions g 2 p,n and g 1 p,n have been recently measured at the Stanford Linear Accelerator Center (SLAC) End Station A facility by the E155 Collaboration using 48.4 GeV and 38.8 GeV longitudinally polarized electrons incident on longitudinally and transversely polarized ammonia (NH 3 ) and lithium deuteride ( 6 Li 2 H 3 ) targets. The proton and deuteron data are combined to extract the neutron structure functions.

Soft X-ray undulator beam line I411 at MAX-II for gases, liquids and solid samples

We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers. © 1999 Elsevier Science B.V. All rights reserved.

ATM in the home - and - the home area network

The cost of asynchronous transfer mode technology is falling while its deployment is growing. Once regarded as a technology strictly for rates above 100 Mbps, ATM may now be considered for any networking scenario where multimedia and real-time are important. We look at a possible deployment path for ATM technology in the home and explain some of our practical work. These are both based on dumb ATM devices which can be built for low cost. The style of operation and method of control of these dumb devices uses the approach of the ATM Warren. The Warren is a method of building low cost ATM devices and switches where the cost savings are achieved by using fixed VCI values in end stations and by using proxy control from a single processor, rather than local control processors in each device or switch.

The ion beam materials analysis laboratory at the environmental molecular sciences laboratory

The Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy (DOE) collaborative scientific user facility located at Pacific Northwest National Laboratory (PNNL), is completing an accelerator facility dedicated to ion beam modification and analysis of materials. This facility consists of a new 3.4 MV tandem accelerator from National Electrostatic Corporation (NEC), two ion sources including an Alphatross source and a SNICS sputter source, and three beam lines. One of the beam lines (+30° beam line) is dedicated to ultrahigh vacuum (UHV) materials analysis. The end station at this beam line has high-energy ion scattering capabilities including Rutherford backscattering spectrometry (RBS), channeling, nuclear reaction analysis (NRA), and elastic recoil detection analysis (ERDA), as well as electron spectroscopies such as low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). This end station is interfaced with the EMSL sample transfer capability which allows a sample to be synthesized, processed, and characterized in different surface science instruments at EMSL without exposing the sample to air. A commercial high vacuum RC43 end station from NEC has capabilities for RBS, NRA, ERDA, particle induced X-ray and gamma emission (PIXE and PIGE), and is located at the end of the −15° beam line. A custom high vacuum end station is connected to the +15° beam line and is dedicated to ion implantation.

Seismic gravity-gradient noise in interferometric gravitational-wave detectors

When ambient seismic waves pass near and under an interferometric gravitational-wave detector, they induce density perturbations in the Earth, which in turn produce fluctuating gravitational forces on the interferometer's test masses. These forces mimic a stochastic background of gravitational waves and thus constitute a noise source. This seismic gravity-gradient noise has been estimated and discussed previously by Saulson using a simple model of the Earth's ambient seismic motions. In this paper, we develop a more sophisticated model of these motions, based on the theory of multimode Rayleigh and Love waves propagating in a multilayer medium that approximates the geological strata at the LIGO sites, and we use this model to reexamine seismic gravity gradients. We characterize the seismic gravity-gradient noise by a transfer function, $T(f)\ensuremath{\equiv}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{x}(f)/\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}(f),$ from the spectrum of rms seismic displacements averaged over vertical and horizontal directions, $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}(f),$ to the spectrum of interferometric test-mass motions, $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{x}(f)\ensuremath{\equiv}L\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{h}(f);$ here $L$ is the interferometer arm length, $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{h}(f)$ is the gravitational-wave noise spectrum, and $f$ is frequency. Our model predicts a transfer function with essentially the same functional form as that derived by Saulson, $T\ensuremath{\simeq}4\ensuremath{\pi}G\ensuremath{\rho}(2\ensuremath{\pi}f{)}^{\ensuremath{-}2}\ensuremath{\beta}(f),$ where \ensuremath{\rho} is the density of Earth near the test masses, $G$ is Newton's constant, and $\ensuremath{\beta}(f)\ensuremath{\equiv}\ensuremath{\gamma}(f)\ensuremath{\Gamma}(f){\ensuremath{\beta}}^{\ensuremath{'}}(f)$ is a dimensionless reduced transfer function whose components $\ensuremath{\gamma}\ensuremath{\simeq}1$ and $\ensuremath{\Gamma}\ensuremath{\simeq}1$ account for a weak correlation between the interferometer's two corner test masses and a slight reduction of the noise due to the height of the test masses above the Earth's surface. This paper's primary foci are (i) a study of how ${\ensuremath{\beta}}^{\ensuremath{'}}(f)\ensuremath{\simeq}\ensuremath{\beta}(f)$ depends on the various Rayleigh and Love modes that are present in the seismic spectrum, (ii) an attempt to estimate which modes are actually present at the two LIGO sites at quiet times and at noisy times, and (iii) a corresponding estimate of the magnitude of ${\ensuremath{\beta}}^{\ensuremath{'}}(f)$ at quiet and noisy times. We conclude that at quiet times ${\ensuremath{\beta}}^{\ensuremath{'}}\ensuremath{\simeq}0.35--0.6$ at the LIGO sites, and at noisy times ${\ensuremath{\beta}}^{\ensuremath{'}}\ensuremath{\simeq}0.15--1.4.$ (For comparison, Saulson's simple model gave $\ensuremath{\beta}={\ensuremath{\beta}}^{\ensuremath{'}}=1/\sqrt{3}=0.58.)$ By folding our resulting transfer function into the ``standard LIGO seismic spectrum,'' which approximates $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}(f)$ at typical times, we obtain the gravity-gradient noise spectra. At quiet times this noise is below the benchmark noise level of ``advanced LIGO interferometers'' at all frequencies (though not by much at $\ensuremath{\sim}10\mathrm{Hz})$; at noisy times it may significantly exceed the advanced noise level near 10 Hz. The lower edge of our quiet-time noise constitutes a limit, beyond which there would be little gain from further improvements in vibration isolation and thermal noise, unless one can also reduce the seismic gravity gradient noise. Two methods of such reduction are briefly discussed: monitoring the Earth's density perturbations near each test mass, computing the gravitational forces they produce, and correcting the data for those forces; and constructing narrow moats around the interferometers' corner and end stations to shield out the fundamental-mode Rayleigh waves, which we suspect dominate at quiet times.

ID14 'Quadriga', a Beamline for Protein Crystallography at the ESRF.

The ESRF undulator beamline ID14 'Quadriga' is dedicated to monochromatic macromolecular crystallography. Using two undulators with 23 mm and 42 mm periods and a minimum gap of 16 mm installed on a high-beta section, it will provide high-brilliance X-ray beams at around 13.5 keV, as well as a wide tuneability between 6.8 and 40 keV. Based on the Troika concept, this beamline has four simultaneously operating experimental stations: three side stations, EH1, EH2 and EH3, using thin diamond crystals, and an end station, EH4, with a fast-scan double-crystal monochromator. Station EH3 has a kappa-diffractometer, and an off-line Weissenberg camera with a large 80 x 80 cm active area combined with a 2048 x 2048 CCD detector. During data collection the image plates are placed and removed by a robot located inside the hutch using a cassette system. After data collection the image plates are scanned with an off-line drum scanner. Station EH4 is designed for MAD applications, including Xe K-edge anomalous experiments, and is equipped with a 2048 x 2048 CCD detector on a pseudo 2theta arm. A common graphical user interface and a database will be available to cover all aspects of data collection, including strategy optimization. First results on the performance of the optics elements and initial crystallographic results are presented.

The Soft X-ray Scanning Photoemission Microscopy Project at SRRC.

The Synchrotron Radiation Research Center (SRRC) and the Institute of Atomic and Molecular Sciences (IAMS) have initiated a project to construct a scanning photoelectron spectromicroscopy end station at SRRC (SRRC-SPEM). High-brightness soft X-rays will be provided by the U5 undulator beamline. Zone-plate-based soft X-ray optics will be used to focus the beam to form the microprobe. A hemispherical sector analyser with multichannel detection capability will collect the photoelectrons. A total of up to 32 images can be acquired concurrently. The apparatus is also equipped with a sample distribution system for in situ sample preparation and characterization in conjunction with other surface spectroscopic techniques.