Inverse Modulation Research Articles

Polarization-independent amplification and frequency conversion in strongly-birefringent fibers

The inverse modulation interaction is a degenerate four-wave mixing process in which two strong pumps drive a weak signal, whose frequency is the average of the pump frequencies. Theoretical analyses and numerical simulations of this process are made for wave frequencies that are near the zero-dispersion frequency of a fiber, in which case dispersion is unimportant, and wave frequencies that are far from the zero-dispersion frequency, in which case dispersion is important. The results show that the inverse modulation interaction in a strongly-birefringent fiber amplifies a linearly-polarized signal by an amount that depends on its phase angle, but not its polarization angle. Phase conjugation and Bragg scattering are nondegenerate four-wave mixing processes in which two strong pumps drive a weak signal and a weak idler. Studies show that phase conjugation and Bragg scattering in strongly-birefringent fibers produce polarization-independent phase-insensitive amplification and frequency conversion, respectively.

Electron transport in silicon nanowires: The role of acoustic phonon confinement and surface roughness scattering

We investigate the effects of electron and acoustic phonon confinements on the low-field electron mobility of thin, gated, square silicon nanowires (SiNWs), surrounded by SiO2. We employ a self-consistent Poisson–Schrödinger–Monte Carlo solver that accounts for scattering due to acoustic phonons (confined and bulk), intervalley phonons, and the Si/SiO2 surface roughness. The wires considered have cross sections between 3×3 and 8×8 nm2. For larger wires, the dependence of the mobility on the transverse field from the gate is pronounced, as expected. At low transverse fields, where phonon scattering dominates, scattering from confined acoustic phonons results in about a 10% decrease in the mobility with respect to the bulk phonon approximation. As the wire cross section decreases, the electron mobility drops because the detrimental increase in both electron-acoustic phonon and electron-surface roughness scattering rates overshadows the beneficial volume inversion and subband modulation. For wires thinner than 5×5 nm2, surface roughness scattering dominates regardless of the transverse field applied and leads to a monotonic decrease in the electron mobility with decreasing SiNW cross section.

A cognitive neuroscience approach to individual differences in sensitivity to reward

The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activation System, defines individual differences on the subject's sensitivity and reactivity to appetitive stimuli associated with mesocorticolimbic structures, while this system does not mediate aversive stimulus processing. However, Jeffrey A. Gray's model also predicts the system's antagonism between this appetitive system and another aversive stimulus sensitive system, the Behavioral Inhibitory System/Fight-Flight-Freeze System, mostly associated with limbic structures. Therefore, direct modulation of brain activation during appetitive stimulus processing should be expected from the Behavioral Activation System, while inverse modulation during aversive stimulus processing may be expected to reflect the system's antagonism. Using the Sensitivity to Reward scale of the SPSR questionnaire to assess individual differences in the activity of the reward system, we present different behavioral and neuroimaging data to illustrate our view. The first experiment was based on a simple letter-judgment task while viewing erotic and aversive pictures selected from the International Affective Picture System. A second experiment employed a task performed by participants to detect infrequent aversive (i.e., stop) signals when responding to reward. The results from these studies were consistent with the idea that Behavioral Activation System-related personality traits mediate the brain activation associated with appetitive stimulus processing in reward-related areas, while it also showed its antagonism to aversive systems through a negative mediation on the limbic cortex activation. To conclude, sensitivity to reward may be understood as a form of impulsivity related to both better appetitive learning and poorer aversive learning.

The Characterization of Moore-Penrose Inverse Module Maps and their Continuity

The Characterization of Moore-Penrose Inverse Module Maps and their Continuity

Dose calculations accounting for breathing motion in stereotactic lung radiotherapy based on 4D-CT and the internal target volume

Purpose The purpose of this study was to determine the 4D accumulated dose delivered to the CTV in stereotactic radiotherapy of lung tumours, for treatments planned on an average CT using an ITV derived from the Maximum Intensity Projection (MIP) CT. Methods For 10 stage I lung cancer patients, treatment plans were generated based on 4D-CT images. From the 4D-CT scan, 10 time-sorted breathing phases were derived, along with the average CT and the MIP. The ITV with a margin of 0 mm was used as a PTV to study a worst case scenario in which the differences between 3D planning and 4D dose accumulation will be largest. Dose calculations were performed on the average CT. Dose prescription was 60 Gy to 95% of the PTV, and at least 54 Gy should be received by 99% of the PTV. Plans were generated using the inverse planning module of the Pinnacle 3 treatment planning system. The plans consisted of nine coplanar beams with two segments each. After optimisation, the treatment plan was transferred to all breathing phases and the delivered dose per phase was calculated using an elastic body spline model available in our research version of Pinnacle (8.1r). Then, the cumulative dose to the CTV over all breathing phases was calculated and compared to the dose distribution of the original treatment plan. Results Although location, tumour size and breathing-induced tumour movement varied widely between patients, the PTV planning criteria could always be achieved without compromising organs at risk criteria. After 4D dose calculations, only very small differences between the initial planned PTV coverage and resulting CTV coverage were observed. For all patients, the dose delivered to 99% of the CTV exceeded 54 Gy. For nine out of 10 patients also the criterion was met that the volume of the CTV receiving at least the prescribed dose was more than 95%. Conclusions When the target dose is prescribed to the ITV (PTV = ITV) and dose calculations are performed on the average CT, the cumulative CTV dose compares well to the planned dose to the ITV. Thus, the concept of treatment plan optimisation and evaluation based on the average CT and the ITV is a valid approach in stereotactic lung treatment. Even with a zero ITV to PTV margin, no significantly different dose coverage of the CTV arises from the breathing motion induced dose variation over time.

Inverse load modulation circuit concept for passive RFID transponder

This paper addresses a new shunt regulation and modulation control concept to reduce parasitic self heating effects and improve communication distances in passive HF RFID systems. A new circuit design for low antenna voltages in RFID tags is presented. For tag to reader communication the principle of inverse load modulation is applied.

Golay Pulse Encoding for Microbubble Contrast Imaging in Ultrasound

We present a technique that uses Golay phase encoding, pulse inversion, and amplitude modulation (GPIAM) for microbubble contrast agent imaging with ultrasound. This technique improves the contrast-to-tissue ratio (CTR) by increasing the time-bandwidth product of the insonating waveforms. A nonlinear pulse compression algorithm is used to compress the signal energy upon receive. A 6.5-dB improvement in CTR was observed using an 8-chip GPIAM sequence compared to a conventional pulse-inversion amplitude-modulation sequence. The CTR improvement comes at the cost of a reduction in frame rate: GPIAM coding uses four input pulses whereas most contrast imaging sequences require two or three pulses. Our results showed that the microbubble response can be phase encoded and subsequently compressed using a nonlinear matched-filtering algorithm, in order to enhance the signal from the contrast agent, while maintaining resolution and suppressing the tissue signal.

Modeling of the inverse base width modulation effect in HBT transistor with graded SiGe base

A model of the position of the edge of emitter-base junction in the base and collector current pre-exponential ideality factor in HBT transistor with a SiGe base is presented. The model is valid for transistors with nonuniform profiles of doping and Ge content. The importance of taking into account the dependence of the effective density of states in SiGe on local Ge content and that of electron diffusion coefficient in SiGe on drift field for modeling accuracy is studied.

Conversion of the LXR-agonist TO-901317—From inverse to normal modulation of γ-secretase by addition of a carboxylic acid and a lipophilic anchor

TO-901317, a LXR agonist, is an inverse modulator of Alzheimer’s disease associated γ-secretase. We synthesized TO-901317 analogous compound but replaced the hexafluorocarbinol moiety by an oxyacetic acid functionality and hypothesized that the replacement would change the mode of action from an inverse modulation to normal modulation of γ-secretase. As anticipated, acid 9 was found to be an effective modulator of γ-secretase and displayed activity at low micromolar concentration. This significant modification can be applied to several inverse γ-secretase modulators. Such modulators may preserve the cleavage of other γ-secretase substrates such as Notch.

Key Issues in integrated seismic exploration

Full seismic inversion, i.e. transforming seismic shot records into geologically oriented subsurface parameters, may be performed by three separate processing modules. In the first module the surface information, i.e. the source input signal and the detector output signals, respectively, are transformed into the downgoing source wavefield and the upgoing reflected wavefield at the surface. Next, the influence of the source wavelet and the surface reflectivity are removed from the wavefields. In the second inversion module, the source wavefield and the reflected wavefield are extrapolated from the surface into the subsurface, and for each subsurface grid point (depth point) the reflectivity is computed. Finally, in the third module, the reflectivity information is transformed into velocity and density maps, and, optionally, into rock and pore parameters. The last step is only feasible if a significant amount of non-seismic information is available. This means that, particularly in the last inversion module, an integrated approach is required. An outline is given of the requirements of an exploration and production (E&P) information management system. It is argued that a fast, single-model database is a prerequisite for management of all related exploration and production data.

GALOIS GROUPS OF MODULES AND INVERSE POLYNOMIAL MODULES

Given an injective envelope E of a left R-module M, there is an associative Galois group Gal<TEX>$({\phi})$</TEX>. Let R be a left noetherian ring and E be an injective envelope of M, then there is an injective envelope <TEX>$E[x^{-1}]$</TEX> of an inverse polynomial module <TEX>$M[x^{-1}]$</TEX> as a left R[x]-module and we can define an associative Galois group Gal<TEX>$({\phi}[x^{-1}])$</TEX>. In this paper we describe the relations between Gal<TEX>$({\phi})$</TEX> and Gal<TEX>$({\phi}[x^{-1}])$</TEX>. Then we extend the Galois group of inverse polynomial module and can get Gal<TEX>$({\phi}[x^{-s}])$</TEX>, where S is a submonoid of <TEX>$\mathbb{N}$</TEX> (the set of all natural numbers).

Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array

Stationary Langmuir probe measurements of ion saturation current and floating potential in a plasma cannot give direct information on density and plasma potential fluctuations in the presence of temperature fluctuations. This problem can be avoided if the probe bias voltage is continuously swept faster than the fluctuation time scale, recording the current-voltage characteristic. This article reports the development of a spatiotemporal highly resolving Langmuir probe array with 15 fast swept tips, operating in the strongly magnetized, collisionless edge plasma of the Wendelstein 7-AS stellarator [Plasma Phys. Controlled Fusion 31, 1579 (1989)]. The probe tips are aligned in the poloidal direction, the tip spacing is 2 mm, and the sweeping frequency is 1.4 MHz. Current and voltage data are sampled with 50 MHz. The high bandwidth of the measurement is achieved by placing miniaturized differential amplifiers close to the probe tips in order to do an impedance transform. The surface-mounting technology and an additional inverse feedback module are utilized, allowing for an input voltage range of +/-100 V, and a common mode rejection rate of 55 dB at 4 MHz, which is sufficient to resolve the nonlinear probe characteristic. For the evaluation of the data, a fit model for stationary probes is employed and found adequate. Changes of the plasma parameters during one voltage sweep are taken into account by a linear interpolation of the fit parameters. Spatio-temporal fluctuation data gained by a fast swept Langmuir probe array, which can be relevant for the turbulent radial transport of particles and energy, are presented.

Electronic and Thermal Properties of Silicon Nanowires

Electron mobility and thermal conductivity of silicon nanowires (SiNWs) of different cross sections were calculated by including scattering of electrons due to confined acoustic phonons, optical phonons, and surface roughness. A reduction in the acoustic phonon group velocity due to the spatial confinement in SiNWs is found to result in lower electron mobility and thermal conductivity compared to the bulk phonon approximation. Among the square SiNWs considered, a SiNW of cross section 6 nm x 6 nm was found to have the highest electron mobility due to the interplay of volume inversion and subband modulation.

The Factor Decomposition Theorem of Bounded Generalized Inverse Modules and Their Topological Continuity

In this paper we obtain a Douglas type factor decomposition theorem about certain important bounded module maps. Thus, we come to the discussion of the topological continuity of bounded generalized inverse module maps. Let X be a topological space, x → Tx : X → L(E) be a continuous map, and each R(Tx) be a closed submodule in E, for every fixed x ∈ X. Then the map \( x \to T^{ + }_{x} :X \to L{\left( E \right)} \) is continuous if and only if \( {\left\| {T^{ + }_{x} } \right\|} \) is locally bounded, where \( {T^{ + }_{x} } \) is the bounded generalized inverse module map of Tx. Furthermore, this is equivalent to the following statement: For each x0 in X, there exists a neighborhood U0 at x0 and a positive number λ such that \( {{\left( {0,\lambda ^{2} } \right)} \subseteq \cap _{{x \in U_{0} }} C} \mathord{\left/ {\vphantom {{{\left( {0,\lambda ^{2} } \right)} \subseteq \cap _{{x \in U_{0} }} C} {\sigma {\left( {T^{ * }_{x} T_{x} } \right)}}}} \right. \kern-\nulldelimiterspace} {\sigma {\left( {T^{ * }_{x} T_{x} } \right)}}, \) where σ(T) denotes the spectrum of operator T.

Inverse and distinct modulation of tau‐dependent neurodegeneration by presenilin 1 and amyloid‐β in cultured cortical neurons: evidence that tau phosphorylation is the limiting factor in amyloid‐β‐induced cell death

Alzheimer's disease (AD) is characterized by massive neuron loss in distinct brain regions, extracellular accumulations of the amyloid precursor protein-fragment amyloid-beta (A beta) and intracellular tau fibrils containing hyperphosphorylated tau. Experimental evidence suggests a relation between presenilin (PS) mutations, A beta formation, and tau phosphorylation in triggering cell death; however, how A beta and PS affect tau-dependent degeneration is unknown. Using herpes simplex virus 1-mediated gene-transfer of fluorescent-tagged tau constructs in primary cortical neurons, we demonstrate that tau expression exerts a neurotoxic effect that is increased with a construct mimicking disease-like hyperphosphorylation [pseudohyperphosphorylated (PHP) tau]. Live imaging revealed that PHP tau expression is associated with increased perikarya suggesting the development of a 'ballooned' phenotype as a specific feature of tau-mediated cell death. Transgenic expression of PS1 suppressed tau-induced neurodegeneration. In contrast, A beta amplified degeneration in the presence of wt tau but not of PHP tau. The data indicate that PS1 and A beta inversely modulate tau-dependent neurodegeneration at distinct steps. They indicate that the mode by which PHP tau causes neurotoxicity is downstream of A beta and that tau phosphorylation is the limiting factor in A beta-induced cell death. Suppression of tau expression or inhibition of tau phosphorylation at disease-relevant sites may provide an effective therapeutic strategy to prevent neurodegeneration in Alzheimer's disease.

Statistical analysis of the results of champ occultation data processing at Shanghai astronomical observatory

With the development of the CPS (Global Positioning System) it has become possible to retrieve accurate profiles of atmospheric temperature, pressure and moisture from CPS occultation data. Using the inversion module developed in Shanghai Astronomical Observatory, (SHAG), we obtained atmospheric profiles from more than 2700 CHAMP occultation events observed in the period 2002 Aug. 1–17. The retrieved profiles are compared with the data of the European Center for Medium-range Weather Forecasts (ECMWF), and their errors are analyzed. An optimal method of statistical analysis is proposed and applied. The statistical results show that GPS occultation data may contribute valuably to numerical weather forecast and long-term monitoring of the earth's climate.

Intravenous immunoglobulin (IVIG)‐mediated neutralisation of C5a: a direct mechanism of IVIG in the maintenance of a high FcγRIIB to FcγRIII expression ratio on macrophages

Intravenous immunoglobulin (IVIG) is used widely in the treatment of various autoimmune conditions. Despite its frequent use, the immunomodulatory mechanism of IVIG is still not fully clear. Recently, the ratio of activating immunoglobulin G Fc receptors (FcγRI, FcγRIII and FcγRIV) and the inhibitory FcγRIIB expression on macrophages was shown to be a key to the therapeutic action of IVIG, as IVIG can cause a high FcγRIIB:FcγRI/III/IV ratio in mouse models of disease (Bruhns et al, 2003; Kaneko et al, 2006). On the other hand, neutralisation of the C3a and C5a complement activation products is another pathway in the action of IVIG (Basta et al, 2003). Previously, it was demonstrated that C5a is a major regulator of the balanced FcR system in both FcR-mediated inflammation (Shushakova et al, 2002) and autoimmunity (Kumar et al, 2006) in mice. Anti-C5aR antibodies and FcγR blocking agents each mimic the anti-inflammatory action of IVIG in vivo (Skokowa et al, 2005), indicating that IVIG may produce its FcγR modulatory effects directly at the level of C5a, but molecular evidence for this possibility is lacking. The present study examined the effect of IVIG on the ability of C5a to differentially regulate FcγR gene expressions in RAW 264·7 macrophage cells transfected with luciferase reporter plasmids containing either the FcγRIIB (−727/+585) or FcγRIII (−1117/+18) gene promoter sequences. Optimal responses of enhanced versus suppressed FcγRIII and FcγRIIB promoter activities in transfected RAW 264·7 cells were obtained by stimulating them with 4·6 nmol/l C5a (50 ng of rhC5a; Sigma-Aldrich, Steinheim, Germany) for 2–4 h (data not shown). These data indicate that C5a activates inverse FcγR regulation in macrophages, confirming previous findings in FcγR mRNA and protein detection assays (Shushakova et al, 2002; Skokowa et al, 2005). We then stimulated macrophages for 4 h with rhC5a in the presence of increasing amounts of IVIG (Octagam®; Octapharma, Langenfeld, Germany). IVIG at 22·5 nmol/l fully blocked the upregulation of FcγRIII and suppression of FcγRIIB gene activities by C5a (Fig 1). We also performed controls to determine the specificity of the blocking effects of IVIG. The cytokine interferon-γ (IFN-γ) exhibits a similar capacity to C5a in triggering inverse FcγR modulation (Radeke et al, 2002). In contrast to C5a, however, FcγR gene regulation induced by IFNγ was not inhibited by IVIG (Fig 1A), indicating selective binding between IVIG and C5a, but not IFNγ, as recently suggested (Basta et al, 2003). Finally, we tested the efficacy of additional IVIG preparations, including a second batch of Octagam®, as well as Beriglobin® (Aventis, Marburg, Germany) and gamunex® (Bayer Vital, Leverkusen, Germany). As shown in Fig 1B, all these IVIG preparations were equally effective (at 22·5 nmol/l) in reversing the C5a-induced upregulation of FcγRIII and downregulation of FcγRIIB genes in macrophages. C5a-induced upregulation of FcγRIII and downregulation of FcγRIIB on macrophages is reversed in the presence of intravenous immunoglobulin (IVIG). (A, B) RAW 264·7 cells were transfected with the indicated FcγRIII (−1117/+18) (left panels) and FcγRIIB (−727/+585) (right panels) promoter constructs plus the renilla luciferase gene as control. After 48 h, an equal volume of complete medium or medium supplemented with 4·6 nmol/l rhC5a and interferon-γ (300 U) in the presence or absence of the indicated doses of IVIG (Octagam®) was added to the cells. (B) In further experiments, FcR-transfected RAW 264·7 cells were stimulated with 4·6 nmol/l rhC5a in the presence of a fivefold molar excess (22·5 nmol/l) of IVIG obtained from different manufacturers (Octagam®, gamunex®, Beriglobin®). (A, B) After an additional 4 h of culture, luciferase activity in the cell lysates was determined by luminescence spectroscopy. Results represent means ± SEM of firefly luciferase counts normalised to renilla luciferase of 6–8 (in A) or 2 (in B) independent transfections. Significant differences were determined by Student's t-test (*P < 0·02; **P < 0·001). The study by Bruhns et al (2003) discussed an indirect mechanism by which IVIG may cause a high FcγRIIB expression level. In that model, IVIG interacted with an as yet undefined receptor on sensor cells to result in the release of mediators capable of inducing expression of FcγRIIB on macrophages. In line with the observations by Basta et al (2003), however, our data now indicate that IVIG-mediated neutralisation of C5a is critical for a sustained high FcγRIIB:FcγRIII ratio expression on macrophages, supporting a more direct mechanism of IVIG in the FcγRIIB-based immune suppression of antibody-dependent autoimmune diseases.

Optimization of the matrix inversion tomosynthesis (MITS) impulse response and modulation transfer function characteristics for chest imaging

Matrix inversion tomosynthesis (MITS) uses linear systems theory, along with a priori knowledge of the imaging geometry, to deterministically distinguish between true structure and overlying tomographic blur in a set of conventional tomosynthesis planes. In this paper we examine the effect of total scan angle (ANG), number of input projections (N), and plane separation/number of reconstructed planes (NP) on the MITS impulse response (IR) and modulation transfer function (MTF), with the purpose of optimizing MITS imaging of the chest. MITS IR and MTF data were generated by simulating the imaging of a very thin wire, using various combinations of ANG, N, and NP. Actual tomosynthesis data of an anthropomorphic chest phantom were acquired with a prototype experimental system, using the same imaging parameter combinations as those in the simulations. Thoracic projection data from two human subjects were collected for corroboration of the system response analysis in vivo. Results suggest that ANG=20 degrees, N=71, NP=69 is the optimal combination for MITS chest imaging given the inherent constraints of our prototype system. MITS chest data from human subjects demonstrates that the selected imaging strategy can effectively produce high-quality MITS thoracic images in vivo.

Differential patterns of multisensory interactions in core and belt areas of human auditory cortex

The auditory cortex is anatomically segregated into a central core and a peripheral belt region, which exhibit differences in preference to bandpassed noise and in temporal patterns of response to acoustic stimuli. While it has been shown that visual stimuli can modify response magnitude in auditory cortex, little is known about differential patterns of multisensory interactions in core and belt. Here, we used functional magnetic resonance imaging and examined the influence of a short visual stimulus presented prior to acoustic stimulation on the spatial pattern of blood oxygen level-dependent signal response in auditory cortex. Consistent with crossmodal inhibition, the light produced a suppression of signal response in a cortical region corresponding to the core. In the surrounding areas corresponding to the belt regions, however, we found an inverse modulation with an increasing signal in centrifugal direction. Our data suggest that crossmodal effects are differentially modulated according to the hierarchical core-belt organization of auditory cortex.

Control of Optical Gain in the Active Region of Quantum Cascade Laser by Strong Perpendicular Magnetic Field

The optical gain in the active region of quantum cascade laser in an external magnetic field is analyzed. When the magnetic field is applied in the direction perpendicular to the plane of the layers, electron dispersion is broken into series of discrete Landau levels. This additional confinement strongly modifies the lifetime of electrons in the upper state of the laser transition, which is controlled by electron-phonon scattering. Landau levels are magnetically tuneable and, depending on their configuration, phonon emission is either inhibited or resonantly enhanced. This translates into a strong modulation of the population inversion, and consequently of the optical gain by varying the magnetic field. Numerical results are presented for a structure previously considered by Smirnov et al. [Phys. Rev B 66 (2002) 125317] which is designed to emit radiation at λ~11.4µm, with the magnetic field varied in the range 10-60T. The effects of band nonparabolicity are taken into account in this model.