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In this report we present preliminary results towards developing an efficient numerical scheme for computing photon migration in complex scattering media such as body tissues. Our motivation for these studies is the appreciation that development of practical imaging schemes will require that solutions to the forward problem be computationally tractable, physically accurate and have a format that maps well to the inverse problem. The object here is to optimize the tradeoffs and still obtain an acceptable answer. It is known, for example, that Monte Carlo methods can provide accurate estimates of photon distributions, even for complex media, but the computing times can be unacceptable long. Numerical solutions to the diffusion are computationally much more efficient, but of course, the physically accuracy of these solutions are subject to the constraints of the diffusion approximation (i.e., away from boundaries and source and the absence of strong discontinuities). We further recognize that for iterative inversion methods, solution of the forward problem on a uniform grid is desirable, as it permits use of global instead of local interpolation functions. Solutions to the forward problem that employ nonuniform grids certainly can be considered, but add to computing times for the inverse problem.

It is desirable for QCM response time (time to measure a frequency change Δf) to be as short as possible, particularly for newer applications of QCM technology such as biochemistry, environmental monitoring for explosives, intrusion detection as well as a microbalance. A new method for making high resolution, rapid frequency measurements is described. The method is applicable for uncoated or functionalized crystals, as the application demands. For a 5 MHz crystal a conservative estimation time for a Δf of 0.1 Hz is less than 1 msec.

The application of III–V semiconductor lasers in telecommunication systems is today an established technique for long haul data transmission. In optical fiber transmission links with data rates up to 2.5 Gbit/s (“data highways”) directly driven DFB lasers are used as transmitters. During the last years 1.3 μm and 1.55 μm DFB laser diodes have maturated from experimental devices to commercial products. In this paper several actual devices for telecommunication systems will be described. Single mode diode lasers might be also attractive for other applications, e.g. spectroscopy in the near infrared [D.E. Cooper and R.U. Martinelli, Laser Focus World 133 (Nov. 1992)]. For this purpose tuning properties of DFB lasers are very important. Typical thermal tuning and current tuning schemes will be discussed. However, single mode lasers are only available for very few specific wavelengths which generally do not coincide with the absorption lines of interesting gaseous species. A few nm tuning range can be achieved changing operation temperature. Larger wavelength ranges can be achieved with tunable lasers currently under development for future telecommunication systems. Widely tunable single mode lasers appear a very promising light source for tunable diode laser spectroscopy.

From the fact that massive Yang-Mills theory can be rewritten as a gauge invariant nonlinear σ-model we derive in a large N limit (N = 4 in the S.M.) the parameters of the S.M. Higgs sector which appears below a typical momentum scale of order 1.2 TeV. The Higgs mass becomes m H = 3v ≌ 426 GeV . The symmetry breaking effect of the large top mass plays a major role in our formalism.

It is shown that in a two scale confining substructure model for Standard Model fermions and weak bosons respectively where the two scale obey Λ ′ ⪢ Λ a see-saw scale μ ≪ Λ , Λ ′ ( μ = Λ · ( Λ / Λ ′)) is generated. We discuss the possible existence of a critical value μ c of μ where, due to an effect of level repulsion, the low energy part of the effective bound state theory lives at the Higgs-confinement phase boundary. Then μ c is identified with the weak scale. We present correlators to be measured at the phase boundary in a lattice definition of the model to determine the mass ratio m Higgs / M W . We argue that by the Weinberg-Witten theorem only the Higgs phase is accessible and a light Higgs exists at the phase boundary. An argument that its effective renormalized couplings are weak is given.

The successful preparation and mode behavior analysis of buried double-heterostructure distributed-feedback (DFB) PbEuSe lasers using an embossing technique for the DFB submicrometer grating is reported here for the first time. The submicrometer grating was embossed with a silicon master grating. By our analysis of the mode spectra using a transfer matrix method, it was possible to distinguish precisely different positions of the laser facets due to the accidental cleaving relatively to the submicrometer grating. >

In this paper, we describe new methods for the simulation, measurement and representation of sEMG signals. With regard to simulation, we choose a 2-D state space model and suggest a 3-D model which can account for in- homogeneities, nonlinearities and memory in the medium and which can be hardware accelerated through FPGA. With regard to measurement we use surface electrodes with a new amplifier circuit topology, which mitigates the effects of pickup and artifacts. With regard to representation, we describe a method for using wavelets which shows promise for isolating signals of interest.

We consider models where the top mass is built up both from a top condensate and radiative contributions and mass generation in the weak boson sector is dynamical. As a consequence charged and neutral pseudo-Goldstone bosons appear. Their masses are estimated and found to be in a range accessible at LHC/SSC. Also they fall naturally in the region where the standard model requires new physics to appear. A brief qualitative discussion concerning their observability is added. Basically the search can be performed together with the search for charged and neutral Higgses. Particular important would be to discriminate them from SUSY charged Higgses. It is noted that the predicted scalar spectrum cannot be imitated by an extended Higgs sector of the standard model. Extension of the radiative mass generation to the τ-sector calls for the introduction of a new heavy lepton doublet with mass in the region 1–2 TeV.

The quark and lepton masses in the second and third family exhibit a correlation with the electric charge such that the state with the bigger charge is the more massive one. In particular the top quark is extraordinarily heavy. We try to understand this for the third family as a result of reaching or not criticality for condensate formation in the various charged channels. As a result mb and mτ are of only radiative origin. We attempt to embed this proposal consistently into a two-scale model of composite quarks, leptons and weak bosons and find that the mass ratio m b m τ is reproduced within a factor of two in a crude one-loop order of magnitude estimate. We also discuss the hypothetical situation with no charge superselection rule operative. A new generation of very heavy leptons with no quark partners is predicted.

We discuss the possibility that in the Wilson lattice definition of confining gauge theories without Goldstone bosons one may systematically adjust the lightest vector mass to zero while keeping the isosinglet scalar mass, which arises by the chiral anomaly, nontachyonic. We discuss a Weyl fermion theory and find the lightest vector particle to be an isoscalar (at least in strong coupling) so that there is no collision with known theorems. We discuss how an abelian gauge symmetry can arise as an infrared attractor and point out a difference between the Weyl fermion theory and one flavour QCD. Attention is also drawn to a physical motivation.

Within a simple model of composite quarks and leptons we present arguments in favour of having a special phase structure for three generations. In fact only in this case one may obtain massless quarks and leptons together with a mass gap in the other channels. The rigorous formulation of the model and a strategy for a simplified calculation of the critical number of massless fermions are described. Other physical features of the model testable at forthcoming accelerators are pointed out.

We discuss some aspects of compositeness related to the hypothesis that the weak boson system represents a mass protected bound state. We present a framework which possesses a nonperturbative lattice regularization where no No-go theorems valid for QCD like theories deny this possibility a priori. Above the weak bosons one more “light” isotriplet vector boson with some peculiar properties, presumably easy to distinguish experimentally, is predicted. Combination with a model of quark-lepton compositeness allows for heuristic arguments suggesting that three generations might be prefered over other numbers of replica. The arguments can in principle be sharpened in a nonperturbative formulation of the model.

We present a two scale chiral model that combines quark-lepton compositeness with composite weak bosons. Asymptotic freedom restricts the number of generations to at most four. The fourth generation is unlikely to occur because in this case the two-loop β-function exhibits an IRSFP in the perturbative region. It is argued that then the largest possible number of generations, N F =3, is the most likely one to be realized because it implies the strongest fermionic screening to suppress chiral condensates. A gauge invariant lattice regularization as a tool for a rigorous nonperturbative investigation is presented and briefly discussed.

An algorithm for the calculation of the propagation constant of integrated-optics waveguides is developed. The waveguide may consist of any number of layers with complex refractive indexes due to gain and loss. It allows the additional determination of the field distribution. Thus, all parameters necessary for heterostructure laser development can be calculated. The resulting program was run on a personal computer; numerical results are presented. >

The authors recently reported the integration of a SIBH laser and an invertible heterobipolar transistor as an emitter follower in a 600-Mb/s OEIC (optoelectronic integrated circuit) on n-doped InP substrate. By optimization of the transistor's base doping and the transistor geometry, an improvement of the frequency behavior has been achieved. The DC characteristic should be sufficient for application in an integrated circuit. together with the results of the 1.5- mu m SIBH laser on semi-insulating InP this appears to be a good basis for the realization of a transmitter OEIC consisting of a laser and a differential amplifier electronic circuit including resistors and capacitors. >

The authors describe a novel technique for imaging in random media using a neural network approach based on a modified backpropagation algorithm. Simulation results indicate that it is possible to produce images of simple structures in 2-D media with a reasonable computation time. The present approach is computation-intensive and for this reason the authors have developed a machine architecture and a machine, Kilonode, which is well suited to this class of computing problems, and which can ultimately be produced at a cost which is suitable for commercial application of the neural network algorithms. >

Double‐channel double‐heterostructure (DCDH) lead chalcogenide lasers were made using a chemical etchant. The etching rate depends strongly on the europium content of the ternary compound PbxEu1−xSe. This technique allows the development of selective etching processes for advanced laser design. The DCDH lasers show low‐threshold current densities of 60 A/cm2 at 20 K and suppression of lateral modes.

The successful preparation of double-heterostructure (DH) distributed-feedback (DFB) PbEuSe lasers using an embossing technique for the DFB sub-micrometer grating is reported here for the first time. The submicrometer grating was performed in (111) oriented silicon wafers by holographic exposure and argon ion milling. Using a hydrostatic press this grating was embossed into a lead chalcogenide wafer, covered by a DH structure grown by molecular beam epitaxy. Lasers made from wafers with grating periodicities of 0.678 and 0.755 Mym show DFB characteristics at the corresponding emission wavenumbers around 1420 and 1590 cmhighminus1.

Buried heterostructure (BH) lasers with a PbSe active layer and Pb 0.97 Eu 0.03 Se confinement layers were fabricated using molecular beam epitaxy (MBE). The waveguide was defined by photolithography and an ion milling process. By MBE overgrowth of the etched structure with a PbEuSe layer the BH-laser was formed. The lasers operated cw with low threshold currents (8 mA at 80 K) in the spectral range from 1280 cm −1 (30 K) to 1800 cm −1 (160K). The spectral characteristics of these lasers were superior to comparable DH stripe lasers. These lasers were the first with IV/VI-MBE overgrowth process of etched lateral structures.

We quantize (1+1)-dimensional quantum chromodynamics on a null plane in the lightlike gauge, using a Hamiltonian formulation. Those parts of the total Hamiltonian which lead to the stringlike eigenstates of the hadrons are identified. It is seen very transparently that the 1/N expansion cannot work for baryons. The physics contained in the rest of the Hamiltonian is exhibited. It is argued that in the small-momentum region the baryon wave function must contain a gauge-invariant admixture of quark-antiquark pairs.

Within a simple model of a self-interacting quark field an attempt is described to introduce diquarks a priori by spontaneous breaking of gauge invariance much in the same way as electron pairs are incorporated by the nonrelativistic BCS theory of superconductivity. This is done because baryons can be regarded as a quark-diquark system. It is shown that quarks with a mass smaller than the invariant mass gap will find it energetically unfavourable to enter a superconducting region. By referring to the Boson transformation method it is argued that bag, respectively, vortex type solutions exist. The quark-quark pairing in the groundstate induces a spontaneous breaking of Lorentz isotropy which, by the Goldstone theorem, leads to automatically confined (abelian) vector gluons of zero mass in the skin region of the hadron. A large anomalous spin-spin coupling among the valence quarks, as required by the π-ϱ mass difference, is likely to be present. It is pointed out that the skin region of mesons and baryons may have a different structure. Solutions where the quark moves freely inside a confined region correspond to the possibility of having a space dependent mass gap.

It is speculated on possible consequences of the scaling behaviour of the quantities υW 2 p (υ,Q 2 ),υW 2 y (υ,Q 2 and σ e + e − tot (s) in the framework of the renormalization group. In order to be able to apply this framework in the timelike region we assume throughout this paper that we are in a truely asymptotic regime, hence far off any threshold.

Hadron-quark reciprocity together with an available fit of the quark-parton distribution functions from electroproduction is used to derive detailed predictions for multiplicities and average multiplicities for electroproduction and annihilation inclusive processes with one nucleon detected in the final state.

Within the framework of Harari’s conjecture and the constraints provided by duality we investigate the consequences of a non-SU3 singlet pomeron in deep inelastic lepton-hadron scattering. The corresponding distribution functions of the quark-parton model are discussed.

We study essentially the states \(\left( {q\bar q} \right)\left( {q\bar q} \right)\) and \(\left( {\bar q\bar q} \right)\left( {qq} \right)\) (baryonium) in the planar approximation in two-dimensional quantum chromodynamics quantized on a null plane. Our results disagree with those of a two-dimensional string model advanced in the literature. In the large-N limit \(\left( {q\bar q} \right)\left( {q\bar q} \right)\) has no bound state. Baryonium is not an eigenstate of the Hamiltonian. The various potential strengths in the four-quark molecules are exhibited.

Two three-triplet models were previously developed to decouple the neutral current from the elastic neutrino vertex, and were investigated for their consequences in deep inelastic lepton-hadron scattering. Lower bounds on the mass of the axial-vector form factor are obtained, which serve to discriminate between the two models. (LBS)

Gain margin and phase margin are important quantities in the description of the performance of feedback systems since they are an accurate measure of relative stability. Their usefulness lies in the fact that they are easily calculated and that their variation with changes in system parameters is easily determined.

We discuss for a nonabelian gauge theory with only left handed fields in the continuum the lattice regularization. Global gauge invariance is kept and we argue that, if perturbative scaling according to the one loop β-function for a dimensionful and physical quantity is observed, the theory behaves as being effectively gauge invariant. Measurable signatures for an intermediate, approximative restoration of local gauge invariance and a problem of the requirement of reflection positivity are discussed.

The local anesthetics bupivacaine, etidocaine, lignocaine and chloroprocaine were infused intravenously for 30 min to pregnant sheep, prepared for chronic studies. The amide compounds reached highere plasma concentrations than chloroprocaine. All local anaesthetics decreased uterine blood flow and O2 consumption without marked alterations of arterial or uterine venous blood gases. These changes were within the wide physiological range of variation, which was established in controls during 24 h. The findings may be of significance during paracervical block or pathological states of UBF or fetal homeostasis.

11 non-pregnant sheep were prepared for chronic studies with an electromagnetic flow transducer placed around one uterine artery and with catheters in both uterine veins, aorta and inferior vena cava. The 4 local anaesthetics bupivacaine, etidocaine, lignocaine and chloroprocaine were infused intravenously on consecutive days in a randomized manner. During the infusions of all 4 local anaesthetics, uterine blood flow decreased due to an increase of uterine vascular resistance. The uterine arteriovenous O2-difference increased, while the uterine O2-consumption decreased without development of an acidosis of the uterus. The same changes were observed in 8 animals, to which oestrone had been administered intravenously prior to the infusions of local anaesthetics. Local anaesthetics had the same effects in the non-pregnant and pregnant uterus. A direct vasoconstrictive mechanism on the uterine vessels as well as a depressing effect on metabolism is discussed for the local anaesthetics.