Maximum Phase Shift Research Articles

Periodic Signal Transmission through Metabolic Pathways with Michaelian Kinetics

The propagation of oscillations in metabolite concentrations mediated by simple Michaelis-Menten enzymes is studied from a theoretical viewpoint. Sinusoidal input waves are investigated, and the resulting output velocities are analyzed. As a first approach, both irreversible and reversible reactions with linear kinetics are examined. Analytical expressions result for the ratios of output to input amplitudes (damping factors), as well as for phase shifts. It is shown that transmission of sinusoidal oscillations by Michaelis enzymes is approximately linear around the mean input flux even for high amplitudes of the velocity. Accordingly, contributions of superior harmonics to the overall waveform can be neglected. The predicted maximum phase shift for these systems is a quarter of a cycle per reaction step, which occurs at high frequencies, Effective rate constants are introduced that are needed for the accurate prediction of output amplitudes. By using them, calculations are presented suggesting that complete transmission can be expected for low- or medium-saturated glycolytic enzymes.

A 10- to 21-GHz, low-cost, multifrequency, and full-duplex phased-array antenna system

This paper presents a novel phased-array antenna system with multifrequency, full-duplex operation, and wide-beam scanning. The system consists of a wideband power divider, a low-loss and low-cost multiline phase shifter controlled by dual piezoelectric transducers (PETS), a four-channel multiplexer, microwave monolithic integrated circuit (MMIC) amplifiers, and a stripline-fed Vivaldi antenna array. The multiline PET phase shifter has a low perturbation loss of less than 2 dB and a total loss of less than 4 dB up to 40 GHz, with a maximum phase shift of 650/spl deg/. Using dual-aligned PETS for bidirectional phase shifting results in wide scan angles of 38.6/spl deg/, 37.6/spl deg/, 43/spl deg/, and 40/spl deg/ for the four channels at 10, 12, 19, and 21 GHz, respectively. The four-channel diplexer demonstrates low insertion loss with high isolation between channels. The new multifrequency phased-array system provides wide-beam scanning and full-duplex capability using a simple, low-cost architecture. The system can be used for applications in mobile satellite communications.

Realization of true-time delay lines based on acoustooptics

A true-time optical delay line for short radiofrequency (RF) pulses using path length dispersion is proposed. It is an optical implementation of the linear phase-shift theorem of the Fourier transformation. Acoustooptic signal processing is used for conversion into the optical frequency domain and for spatial Fourier decomposition of the pulse. The processing of the pulse is obtained by differentially phase shifting the particular frequency components, followed by a heterodyne reconversion into the RF domain. The optical system is intended to be used for delaying, but also for shaping and filtering of RF pulses, mainly in phased array radar antennas. Theoretical analysis of the system principle is given together with experimental results, demonstrating 2-/spl mu/s time delay of 0.5-/spl mu/s-long pulses with maximum optical phase shift of 1.2/spl pi/. A detailed theoretical and experimental bandwidth analysis is carried out, pointing to the main technical problems and their solutions.

On T2-shortening by weakly magnetized particles: the chemical exchange model.

Chemical exchange (CE) theory is compared with two theories of T2-shortening caused by microscopic magnetic centers: inner- and outer-sphere relaxation theory (long-echo limit) and mean gradient diffusion theory (short-echo limit). The CE equation is shown to be identical to these theories in the respective limits and appropriate parameter relationships are derived for spherical particles. The theories are then compared with computer simulations of spherical particles and with a recent general theory, with good agreement in the asymptotic regions. The CE model also reproduces the essential relaxation characteristics in the intermediate range. Finally, good agreement of a CE model with simulations for magnetized cylinders is also demonstrated. The discussion is limited to weakly magnetized particles such that the maximum phase shift during an echo interval is less than one radian, permitting the use of the Luz-Meiboom CE equation. Published 2001 Wiley-Liss, Inc.

Multipath scattering from complex targets

Identifying interference patterns originating from particular scatterers on complex objects above an electromagnetic smooth surface can be difficult, especially if the scatterers are not dominant. The author shows the existence of an incoherent scattering space where the relative positions of the scatterers in either height or range are irrelevant and where the backscattered power is the result of an incoherent summation of the reflected fields comprising the target. The incoherent scattering space is defined as that space where the maximum multipath phase shift between the scatterers is smaller than π/2. Owing to the small relative phase shift between the scatterers within this space, the fluctuations of the reflected signal are small and a point reflector may hence substitute the complex target. The existence of the space is determined by the height of the radar antenna, the relative height of the scatterers, the range and the electromagnetic frequency.

Phase tuning of injection-locked VCSELs

Phase tuning of injection-locked single-mode vertical-cavity surface-emitting laser diodes (VCSELs) is investigated experimentally with two slave VCSELs being locked by a master VCSEL. By slightly varying the laser current and thereby the frequency within the locking range, a maximum phase shift of more than 0.8 /spl pi/ is achieved. The method is applicable to large injection-locked VCSEL arrays.

A low-cost 8 to 26.5 GHz phased array antenna using a piezoelectric transducer controlled phase shifter

A new phased array antenna of wide bandwidth and good beam scanning angle has been developed using a low cost multiline phase shifter controlled by a piezoelectric transducer (PET) and a stripline fed Vivaldi antenna array. The multiline progressive PET phase shifter has a low perturbation loss of less than 2 dB and a total loss of less than 4 dB up to 40 GHz with a maximum phase shift of 480/spl deg/. The proposed phased array antenna consists of four E- or H-plane Vivaldi antennas, a PET phase shifter, and a power divider. The phased array shows a wide beam scanning capability of /spl plusmn/27/spl deg/ over a wide bandwidth from 8 to 26.5 GHz covering X, Ku, and K bands.

Structural and dielectric properties of epitaxial Ba1−xSrxTiO3/Bi4Ti3O12/ZrO2 heterostructures grown on silicon

We report on the dielectric properties of an epitaxial heterostructure comprised of Ba1−xSrxTiO3, Bi4Ti3O12, and (ZrO2)0.91(Y2O3)0.09 grown on silicon substrates for potential use in microwave devices. Careful x-ray analysis indicates crystallographic alignment of all layers and transmission electron microscopy and Auger analysis reveals high quality epitaxy with minimal interdiffusion. The viability of using such heterostructures in actual microwave devices was assessed by incorporating the films in a coupled microstripline phase shifter design. The phase shifter devices, operating in the Ku band, had losses of less than 4 dB with a maximum phase shift of nearly 40° at 40 V. We compare this performance with a (Ba, Sr)TIO3/MgO phase shifter. These results presented represent significant progress towards integrating ferroelectric films with conventional silicon technology.

Circadian clock-protein expression in cyanobacteria: rhythms and phase setting.

The cyanobacterial gene cluster kaiABC encodes three essential circadian clock proteins: KaiA, KaiB and KaiC. The KaiB and KaiC protein levels are robustly rhythmical, whereas the KaiA protein abundance undergoes little if any circadian oscillation in constant light. The level of the KaiC protein is crucial for correct functioning of the clock because induction of the protein at phases when the protein level is normally low elicits phase resetting. Titration of the effects of the inducer upon phase resetting versus KaiC level shows a direct correlation between induction of the KaiC protein within the physiological range and significant phase shifting. The protein synthesis inhibitor chloramphenicol prevents the induction of KaiC and blocks phase shifting. When the metabolism is repressed by either translational inhibition or constant darkness, the rhythm of KaiC abundance persists; therefore, clock protein expression has a preferred status under a variety of conditions. These data indicate that rhythmic expression of KaiC appears to be a crucial component of clock precession in cyanobacteria.

Large dielectric constant (ε/ε>6000) Ba0.4Sr0.6TiO3 thin films for high-performance microwave phase shifters

We deposited epitaxial Ba0.4Sr0.6TiO3 (BST) films via laser ablation on MgO and LaAlO3 (LAO) substrates for tunable microwave devices. Postdeposition anneals (∼1100 °C in O2) improved the morphology and overall dielectric properties of films on both substrates, but shifted the temperature of maximum dielectric constant (Tmax) up for BST/LAO and down for BST/MgO. These substrate-dependent Tmax shifts had opposite effects on the room-temperature dielectric properties. Overall, BST films on MgO had the larger maximum dielectric constant (ε/ε0⩾6000) and tunability (Δε/ε⩾65%), but these maxima occurred at 227 K. 30 GHz phase shifters made from similar films had figures of merit (ratio of maximum phase shift to insertion loss) of ∼45°/dB and phase shifts of ∼400° under 500 V (∼13 V/μm) bias, illustrating their utility for many frequency-agile microwave devices.

A low-loss time-delay phase shifter controlled by piezoelectric transducer to perturb microstrip line

This paper presents a new time-delay phase shifter using a piezoelectric transducer (PET) on a microstrip line with computational and experimental results. Dielectric perturbation changes the line capacitance and propagation constant of the microstrip line. The phase of the microstrip line is varied, but insertion loss is not much affected. A maximum phase shift of 460/spl deg/ with respect to the unperturbed condition has been achieved with an increased insertion loss of less than 2 dB and a total loss of less than 4 dB up to 40 GHz, using the dielectric perturbation controlled by PET. The proposed phase shifter should have many applications in antenna beam steering and in other microwave and millimeter-wave circuits.

Magnetic Force Microscope Study on Quick-Quenched Ribbon Sm2Fe14.5Cu0.5Ca2Cx

The microstructure and magnetic domain structures of the annealed quick-quenched ribbon Sm2Fe14.5Cu0.5Ca2Cx were studied by using magnetic force microscope. The results of the topography image and magnetic force image (MFI) show that the grain size is between 2555nm, whereas the domain size is between 200400nm. The magnetic domain length scale is much larger than the grain size. The domain comprises of a lot of grains, which were called interaction domain. The detail analysis such as power spectral density analysis, the maximum phase shift and roughness analyses on the MFI demonstrated that they are connected with the intrinsic magnetic properties such as HA in some way.

Serotonin antagonists do not attenuate activity-induced phase shifts of circadian rhythms in the Syrian hamster

A variety of observations from several rodent species suggest that a serotonin (5-HT) input to the suprachiasmatic nucleus (SCN) circadian pacemaker may play a role in resetting or entrainment of circadian rhythms by non-photic stimuli such as scheduled wheel running. If 5-HT activity within the SCN is necessary for activity-induced phase shifting, then it should be possible to block or attenuate these phase shifts by reducing 5-HT release or by blocking post-synaptic 5-HT receptors. Animals received one of four serotonergic drugs and were then locked in a novel wheel for 3 h during the mid-rest phase, when novelty-induced activity produces maximal phase advance shifts. Drugs tested at several doses were metergoline (5-HT 1/2 antagonist; i.p.), (+)-WAY100135 (5-HT 1A postsynaptic antagonist, which may also reduce 5-HT release by an agonist effect at 5-HT 1A raphe autoreceptors; i.p.), NAN-190 (5-HT 1A postsynaptic antagonist, which also reduces 5-HT release via an agonist effect at 5-HT 1A raphe autoreceptors; i.p.) and ritanserin (5-HT 2/7 antagonist; i.p. and i.c.v.). Mean and maximal phase shifts to running in novel wheels were not significantly affected by any drug at any dose. These results do not support a hypothesis that 5-HT release or activity at 5HT1, 2 and 7 receptors in the SCN is necessary for the production of activity-induced phase shifts in hamsters.

One-dimensional analytical model of the phase shift due to Bragg backscattering of an ordinary wave by large amplitude density fluctuations

The phase shift due to the resonant Bragg scattering of an ordinary wave in a fluctuating plasma is numerically computed for large amplitude density fluctuations, i.e. well beyond the Born approximation. The phase response (the phase shift against the perturbation position in the density gradient) is strongly distorted with respect to the small amplitude case, and phase jumps occur. For localized quasi-monochromatic fluctuations, the results are explained by an analytical model where the Helmholtz equation is approximated by a Mathieu equation. The maximum phase shift and the phase jumps are well predicted by the model. It turns out that the theoretical predictions also apply to moderate amplitudes. For an actual phase measurement where the number of different frequencies (i.e. the number of perturbation positions) is finite, most phase jumps are missed, due to the steepness of the phase jumps, and the measured phase shift increases continuously.

Design of high-frequency ZnO-coated optical fiber acoustooptic phase modulators

In this paper, we present a theory of an optical fiber acoustooptic phase modulator using piezoelectric zinc oxide (ZnO) coating. The effects of changing device parameters in the acoustooptic resonator are investigated for transducer design. These results are entirely different from those of the well-known; planar device structure since every part plays an important role in the resonator structure. Optical phase modulation in the frequency region up to 1 GHz is also demonstrated. Multiple sharp resonance peaks with a maximum phase shift of 0.7 radians are observed.

Nonreciprocal TE-mode phase shift by domain walls in magnetooptic rib waveguides

The nonreciprocal wave number shift of a TE-like mode propagating along a normally magnetized gyrotropic rib waveguide supporting a domain lattice is predicted theoretically using perturbation theory. The electromagnetic fields are calculated by the effective index method and by a more rigorous numerical method. Preliminary estimations for Bi-substituted iron garnets show that the maximum nonreciprocal phase shift of a TE-like mode may be comparable to that of a TM-like mode in a tangentially magnetized waveguide.

All-fiber acoustooptic phase modulators using chemical vapor deposition zinc oxide films

For the first time we report an all-fiber acoustooptic phase modulator using a zinc oxide (ZnO) film deposited by modified single source chemical vapor deposition. This technique allows deposition over the full 360/spl deg/ fiber surface without the need for sample rotation, greatly simplifying the manufacturing process. The maximum phase shift measured for our 6 mm long devices was 3.5 rads for a drive power of 580 mW. Unlike devices fabricated using sputtered ZnO films the maximum attainable phase shift is not significantly limited by thermal and mechanical loss effects at higher driving powers which we attribute to the excellent chemical composition of our chemical vapor deposition (CVD) grown films. A maximum efficiency of 0.28 rad//spl radic/(mW)/cm of device length was measured which may be attributed to the relatively thin films used in this experiment (0.4-0.9 /spl mu/m).

Modeling, Synthesis and Characterization of a Millimeter-Wave Multilayer Microstrip Liquid Crystal Phase Shifter

Electromagnetic simulation software is used for modeling the properties of a 2–15 GHz liquid crystal microstrip phase shifter previously designed at Thomson-CSF. After experimental validation of the computed results, the software is applied to the modeling of a new 30–40 GHz multilayer microstrip phase shifter, where the active medium is a liquid crystal inserted between solid dielectric substrates. Measurements carried out at between 10 and 40 GHz on 4.35 cm long lines are in good agreement with theoretical predictions. A maximum experimental phase shift of 219.3° at 37 GHz (about 50°/ cm) was observed for a structure with a commercial liquid crystal (BDH-E44) and silica substrates.

Vitamin B12 amplifies circadian phase shifts induced by a light pulse in rats.

Vitamin B12 (VB12) is a putative modulator of the human circadian clock, improving entrainability to the 24 h light-dark cycle. The present study was intended to elucidate the mechanism of VB12 action in an animal model. In male rats free-running under constant dim illumination, a single light pulse of 50-1000 lux for 20 min given at circadian time (CT) 20 induced a 0.28 to 1.08 h phase advance and at CT 14 induced a 0.54 to 2.10 h phase delay. A 3 h intracerebroventricular (icv) infusion of 30 nmol VB12 starting 2 h prior to a 20 min 200 lux light pulse significantly amplified phase shifts in comparison with saline-treated or untreated controls. The mean phase advance (1.13 h) was 1.8-fold greater than that of saline-infused controls, whereas the mean phase delay (2.28 h) was 2.9-fold greater. These values were comparable to the maximal phase shifts caused by 1000 lux light pulses in untreated rats. Since the same VB12 treatment alone had failed to induce a phase shift in a previous experiment, these results indicate that VB12 strongly enhanced light pulse-induced phase shifts and thus augmented the entrainability of the circadian clock to light.

Green light evokes maximum phase shifts in the locomotor activity rhythm of the field mouse Mus booduga

The effect of pulses of different monochromatic light wavelengths was investigated on the circadian locomotor activity rhythm of the tropical rodent Mus booduga. Blue (480 nm), green (549 nm) and red (649 nm) light were used for pulses at circadian time (CT) 14 and 20, the maximum delay and advance eliciting phases of the white light phase response curve (PRC). All three wavelengths evoked qualitatively similar responses in terms of the signs of the phase shifts. Contrary to the results obtained in rabbits and bats, M. booduga does not exhibit differential responses to different light wavelengths at various phases. This prompts us to speculate on the existence of a single class of photoreceptors for all light wavelengths. The responses of these animals to three different energy levels (5, 25 and 50 μW cm −2) of these light wavelengths were also studied and these showed quantitative differences. Green light evoked larger phase shifts in terms of both delays and advanced compared with red light ( P<0.1 at both CTs). However, it failed to exhibit an energy-dependent increase in the magnitude of the phase shifts. In contrast, red light evoked an energy-dependent increase in the magnitude of the phase shifts of both CT 14 and CT 20 and blue light at CT 14 alone. It is speculated that the threshold level for perceiving green light may be lower than the energy levels used and hence saturation would have been reached at 5 μW cm 2. For red light, it is possible that this threshold is at a much higher level. This explains the failure to exhibit an energy-dependent increase by green light and the systematic increase by red light.