Transverse Extent Research Articles

Dynamics of narrow electron streams in magnetized plasmas

In this analytical and computer simulation study we explore the dynamics of a narrow electron stream embedded in a magnetized plasma. The transverse dimension of the stream is envisioned to be on the order of the electron skin depth, as is appropriate to several problems of current interest (e.g., auroral beams, reconnection). Within the layer the drift velocity exceeds the thermal velocity, and thus the Buneman instability is excited. The method of matched asymptotic expansions is used to describe the linear stage of the instability for a nonuniform drift profile. It predicts a lowering of the growth rate and a rapid decrease in wave amplitude at the spatial location where the beam mode resonance is encountered. A particle-in-cell (PIC) simulation is used to verify the predictions of the analysis and to illustrate the important nonlinear behavior. It is found that the rapid flash of the Buneman instability excites a lower-hybrid wave, causes strong perpendicular ion acceleration, and results in a region of depleted density. The PIC study also considers a quasisteady situation that models the effect of a shear Alfvén wave of narrow transverse extent.

Anal endosonographic evaluation after closed lateral subcutaneous sphincterotomy.

The present study was undertaken to evaluate anal endosonographic results of the transverse and longitudinal extent of internal anal sphincter division after closed lateral subcutaneous sphincterotomy and its relationship to outcome with respect to anal fissure recurrence and postoperative anal incontinence. Ten patients selected for symptomatic anal fissure recurrence (mean follow-up, 10.9 months) and 41 asymptomatic control patients (mean follow-up, 15.5 months) were reviewed by anal endosonography after closed lateral subcutaneous sphincterotomy. Clinical evaluation was focused on anal fissure recurrence and postoperative anal incontinence. The anal endosonographic study involves serial radial images of the distal, proximal, and midanal canal. In 32 patients in whom a complete internal sphincter defect was identified, 31 (75.6 percent) were from the control group and only 1 patient (10 percent) was from the recurrence group (P < 0.001). In 19 patients, an incomplete internal sphincter defect was identified; 10 (24.4 percent) were from the control group (residual median size, 1.8 mm; contralateral, 2.5 mm) and 9 patients (90 percent) were from the recurrence group (P = 0.001; residual median size, 1.4 mm; contralateral, 2.2 mm). Ten patients (19.6 percent) were incontinent for gas and three patients (5.9 percent) for liquid feces, without significant differences between groups. Anal endosonography is a useful method for evaluating the anatomic effectiveness of closed lateral subcutaneous sphincterotomy. An incomplete sphincterotomy is associated with significant symptomatic anal fissure recurrence.

Organization of direct hippocampal efferent projections to the cerebral cortex of the rhesus monkey: projections from CA1, prosubiculum, and subiculum to the temporal lobe.

This study investigates direct hippocampal efferent projections to the temporal lobe of the rhesus monkey. Tritiated amino acid injections were placed into the hippocampal formation to identify terminal fields, and complementary fluorescent retrograde tracer injections were placed into the cortex to identify the cells of origin. Tritiated amino acid injections into CA1, prosubicular, or subicular subfields produced anterograde label over parts of the parahippocampal gyrus and temporal pole. Injections of fluorescent retrograde tracers demonstrated that these projections originate from longitudinal strips of neurons that occupy part of the CA1 subfield as well as from strips of neurons in adjacent prosubicular and subicular subfields. Thus, an injection into area TH of the posterior parahippocampal gyrus labeled neurons in a longitudinal strip of proximal CA1 (i.e., near CA2) as well as a strip in the subiculum; injections into areas TF, TL, 35, or Pro labeled neurons in a longitudinal strip of distal CA1 (i.e., near the prosubiculum) as well as one in the prosubiculum; and an injection into area TFO labeled neurons in a longitudinal strip in the middle of CA1. These strips of neurons extended longitudinally throughout the entire rostrocaudal length of the hippocampus. These results demonstrate that, in the monkey, CA1 projections to cortex arise topographically from longitudinally oriented strips of neurons that occupy only a part of the transverse extent of CA1 but that cover most of the anteroposterior extent of the hippocampus. Thus, in the monkey, CA1 is not a single uniform entity and may have a unique role as a source of direct hippocampal projections to the cerebral cortex.

Spatially antibunched semiconductor laser beam for sub-shot-noise-limited apertured transmission

It is shown that, using a semiconductor laser, one can generate spatially antibunched light. This light displays a smaller variance when measured over finite spatial regions than light from a classical source. In analogy with the common (temporal) amplitude-squeezed light, which possess photon statistics that are more regularly spaced in time than a Poissonian, this spatially amplitude-squeezed light produces a beam having photon statistics that are more highly correlated across its transverse extent than the typical (having Poissonian detection statistics) laser beam. One may have a spatially amplitude-squeezed source which does not display temporal squeezing, and one may have a temporally amplitude-squeezed source which does not display spatial amplitude squeezing. The possibility of having both forms of amplitude squeezing simultaneously is considered and such a device, using semiconductor laser technology, is proposed. Analysis reveals that there is indeed a quantum correlation between different segments of the beam. This spatially antibunched light suffers less signal-to-noise degradation when spatially partitioned in the object or subsequent image planes, making it potentially superior in spatial light modulation, free-space transmission, or imaging applications.

Formation of spherically polarized Alfvén waves and imbedded rotational discontinuities from a small number of entirely oblique waves

We present two‐and‐one‐half‐dimensional (2½‐D) hybrid numerical simulations of a small group of oblique Alfvén waves with linear polarization. These are the first simulations of nonplanar Alfvén waves which evolve to a nearly constant‐B state (spherical polarization) with imbedded rotational discontinuities (RDs). Initially, B varies with position in the wave group, and we consider only cases where the Fourier components of B2 are entirely oblique to the background magnetic field B0. When propagating in different directions but with group speeds in the same direction along B0, Alfvén waves generally evolve nonplanar waveforms with nearly constant magnetic intensity B. In this waveform, the magnetic field vectors move on a sphere of radius B and have a spherical rather than arc polarization. Most Alfvénic fluctuations in the solar wind are spherically polarized. We also find analytical second‐order solutions from the magnetohydrodynamic equations for linearly polarized Alfvén waves in 2½‐D and 3‐D. For moderate‐wave amplitudes (|δB|/B0 ≲ 0.5), these show that the second‐order driven wave solution can only remove variations of B when the Fourier components of B2 are oblique to B0. Large‐amplitude (|δB|/B0 ∼ 1) waves also evolve to constant magnetic intensity, but higher‐order terms produce imbedded RDs with properties similar to those seen in the solar wind. The RDs are steady, and their normals are oblique to B0. The transverse extent of the RDs is approximately of order of the average wavelength of the Alfvén waves, and the RDs are either locally planar or fully nonplanar. RDs can appear at less than twice per cycle in waveforms composed of two or more waves. If the magnetic fields are sampled along a single line through the simulation box, as a single spacecraft would observe Alfvénic fluctuations in the solar wind, the rate depends on the direction that the line takes through the box. We also suggest that all Alfvénic fluctuations are spherically polarized, and instances of arc‐polarized fluctuations occur when spacecraft sample locally planar structures.

Near-field and far-field propagation of beams and pulses in dispersive media

We formulate an efficient exact method of propagating optical wave packets (and cw beams) in isotropic and nonisotropic dispersive media. The method does not make the slowly varying envelope approximation in time or space and treats dispersion and diffraction exactly to all orders, even in the near field. It can also be used to determine the partial differential wave equation for pulses (and beams) to any order as a power series in the partial derivatives with respect to time and space. The method can treat extremely focused pulses and beams, e.g., from near-field scanning optical microscopy sources whose transverse spatial extent in smaller than a wavelength.

A time dependent solution to the relativistic one-dimensional diode

Work in understanding electron flow across a simple potential gap, a diode, has a long history: The Child-Langmuir law [C. Child, Phys. Rev. 32 (1911) and I. Langmuir, Phys. Rev. 2 (1913) 450] describes the current density achievable in a one dimensional diode in the steady state. Pierce [Theory and Design of Electron Beams (Van Nostrand, Princeton and London, 1949)] extended the work by demonstrating that a beam of charged particles of finite transverse extent will exactly obey the one dimensional law as long as appropriate boundary conditions exterior to the beam are satisfied. Jory and Trivelpiece extended the solution to relativistic energies [J. Appl. Phys. 40 (1969) 3924], and Lampel and Tiefenback presented a solution for a time dependent non-relativistic step function current [Appl. Phys. Lett. 43 (1983) 57]. This paper presents an analytic solution for a voltage waveform across a fully relativistic one-dimensional diode which produces a constant electron current exiting the diode after a time equal to an electron transit time under steady state space charge limited operation. This result is compared to the previous result obtained for the non-relativistic case. Relevance of this solution to single cell RF-guns is discussed.

Jet cocoons and the formation of narrow-line clouds in Seyfert galaxies

We present non-adiabatic hydrodynamic simulations of a supersonic light jet propagating into a fully ionized medium of uniform density on a scale representative of the narrow line region (NLR) in Seyfert galaxies with associated radio jets. In this regime the cooling distance of the swept up gas in the bowshock of the jet is of the same order as the transverse extent of the jet bowshock, as opposed to the more extreme regimes found for more powerful adiabatic large scale jets or the slow galactic jets which have been simulated previously. We calculate the emissivity for the H_alpha line and radio synchrotron emission. We find that the structure of the line emitting cold envelope of the jet cocoon is strongly dependent on the non-stationary dynamics of the jet head as it propagates through the ambient medium. We observe the formation of cloud-like high density regions which we associate with NLR clouds and filaments. We find that some of these clouds might be partially neutral and represent sites of jet induced star formation. The calculated H_alpha flux and the spectral line width are consistent with NLR observations. The simulation of the radio-optical emission with radiative cooling confirms the basic result of the geometric bowshock model developed by Taylor et al. (1989) that the start of noticeable optical line emission can be significantly offset from the hotspot of the radio emission. However, the time-dependent nature of the jet dynamics implies significant differences from their geometric bowshock model.

Spiral CT With Multiplanar and Three-Dimensional Reconstructions Accurately Predicts Tracheobronchial Pathology

This study was designed to evaluate the clinical accuracy of multiplanar reconstructions and three-dimensional shaded surface displays compared with conventional transaxial computed tomography, bronchoscopy, and surgical pathologic findings. Transaxial computed tomographic images, two-dimensional nonstandard multiplanar reconstruction images, and three-dimensional images obtained from patients with tracheobronchial disease were prospectively evaluated for the relationship to adjacent structures, lesion characterization, and surgical anatomic correlation before invasive procedures. Compared with conventional transaxial computed tomographic images, multiplanar reconstructions and three-dimensional shaded surface displays provided a correlative map of bronchoscopic and surgical anatomy in patients with benign and malignant tracheobronchial pathology. The longitudinal extent of abnormalities are better demonstrated on the multiplanar reconstruction and three-dimensional images, whereas the transverse extent of disease and relationships to adjacent structures were better shown on axial computed tomographic sections. Three-dimensional and multiplanar two-dimensional images are additive to transaxial computed tomography for evaluation of diseases involving the central airways. They are beneficial for planning invasive procedures. More importantly, they provide consistent, highly accurate measurements for routine follow-up and for future clinical trials.

Multiple breathhold 3D time-of-flight MR angiography of the renal arteries.

A technique is described for angiographic imaging of the renal arteries with acquisition performed over several periods of suspended respiration. The 3D Fourier transform (FT) gradient-echo angiographic sequence uses magnetization preparation and appropriately chosen delay times for background nulling and time-of-flight enhancement of the vasculature. The sequence was applied to 10 volunteers, each of whom was imaged in three ways: (i) over a series of breathholds in which feedback was provided to enable reproducible breathholding; (ii) over a series of breathholds with no feedback; and (iii) over continuous respiration. Results were evaluated by measuring the transverse extent of the well-delineated renal vasculature and by noting the distal extent of the vasculature branching (main, segmental, and interlobar branches). The transverse extent of renal vasculature visible with breathhold feedback, breathholding, and free breathing was 6.1 +/- 0.9 cm, 5.0 +/- 1.8 cm, and 4.0 +/- 1.4 cm, respectively (mean +/- SD). Breathhold feedback enabled visualization of segmental renal arteries bilaterally in all 10 volunteers.

VLF and LF signatures of mesospheric/lower ionospheric response to lightning discharges

New evidence is presented of disturbances of the electrical conductivity of the nighttime mesosphere and the lower ionosphere in association with lightning discharges. In addition to extensive documentation of the characteristics of a class of events heretofore referred to as early/fast VLF events [Inan et al., 1993], our data reveal a new feature of these events, consisting of a postonset peak that typically lasts for 1–2 s. We also report the observation of short‐duration VLF or LF perturbations, in which the amplitude of the subionospheric signal exhibits a sudden change within 20 ms of the causative lightning discharge, and recovers back to its original level in &lt; 3 s. These short‐duration events have characteristics similar to the previously observed rapid onset, rapid decay VLF signatures [Dowden et al.., 1994]. Both the typical and rapidly recovering events are observed primarily when the causative lightning discharge is within ±50 km of the VLF or LF great circle propagation path, indicating that the scattering from the localized disturbance is highly collimated in the forward direction. The latter in turn implies that for the parameters in hand, the transverse extent of the disturbance must be at least ∼ 100–150 km. The measured VLF signatures are compared with the predictions of a three‐dimensional model of subionospheric VLF propagation and scattering in the presence of localized ionospheric disturbances produced by electromagnetic impulses and quasi‐electrostatic (QE) fields produced by lightning discharges. The rapidly recovering or short‐duration events are consistent with the heating of the ambient electrons by quasi‐static electric fields, in cases when heating is not intense enough to exceed the attachment or ionization thresholds. When no significant electron density changes occur, the conductivity changes due to heating alone last only as long as the QE fields, typically less than a few seconds. When heating is intense enough so that attachment or ionization thresholds are exceeded, reductions or enhancements in electron density can respectively occur, in which case the medium would relax back to the ambient conditions with the time scales of the local D region chemistry, typically 10–100 s.

A quantitative analysis of the dendritic organization of pyramidal cells in the rat hippocampus.

The three dimensional organization of the dendritic trees of pyramidal cells in the rat hippocampus was investigated using intracellular injection of horseradish peroxidase in the in vitro hippocampal slice preparation and computer-aided reconstruction. The total dendritic length, dendritic length in each of the hippocampal laminae, and the number of dendritic branches were measured in 20 CA1 pyramidal cells, 7 neurons in CA2 and 20 CA3 pyramidal cells. The total dendritic length of CA3 pyramidal cells varied in a consistent fashion depending on their position within the field. Cells located close to the dentate gyrus had the smallest dendritic trees which averaged 9,300 microns in total length. Cells in the distal part of CA3 (near CA2) had the largest dendritic trees, averaging 15,800 microns. The CA2 field contained cells which resembled CA3 pyramidal cells in most respects except for the absence of thorny excrescences on their proximal dendrites. There were also smaller pyramidal cells that resembled CA1 neurons. CA1 pyramidal cells tended to be more homogeneous. Pyramidal neurons throughout the transverse extent of CA1 had a total dendritic length on the order of 13,500 microns. The quantitative analysis of the laminar distribution of dendrites demonstrated that the stratum oriens and stratum radiatum contained significant portions of the pyramidal cell dendritic trees. In Ca3, for example, 42-51% of the total dendritic length was located in stratum oriens; about 34% of the dendritic tree was located in stratum radiatium. The amount of dendritic length in stratum lacunosum-moleculare of CA3 varied depending on the location of the cell. Many CA3 cells located within the limbs of the dentate gyrus, for example, had no dendrites extending into stratum lacunosum-moleculare whereas those located distally in CA3 had about the same percentage of their dendritic tree in stratum lacunosum-moleculare as in stratum radiatum. In CA1, nearly half of the dendritic length was located in stratum radiatum, 34% was in stratum oriens and 18% was in stratum lacunosum-moleculare. These studies identified distinctive dendritic branching patterns, in the stratum radiatum and stratum lacunosum-moleculare, which clearly distinguished CA3 from CA1 neurons.

Soft x-ray scanning microtomography with submicrometer resolution

Scanning soft x-ray microtomography was used to obtain high-resolution three-dimensional images of a microfabricated test object. Using a special rotation stage mounted on the scanning transmission x-ray microscope at the X1A beamline at the National Synchrotron Light Source, we recorded nine two-dimensional projections of the 3D test object over an angular range of −50° to +55°. The x-ray wavelength was 3.6 nm and the radiation dose to the object per projection was approximately 2×106 Gy. The object consisted of two gold patterns supported on transparent silicon nitride membranes, separated by 4.75 μm, with 100- to 300-nm-wide and 65-nm-thick features. We reconstructed a volumetric data set of the test object from the two-dimensional projections using an algebraic reconstruction technique algorithm. Features of the test object were resolved to ∼100 nm in transverse and longitudinal extent with low artifact in three-dimensional images rendered from the volumetric set.

922-59 Aortic Inner Surface Morphology in Aortic Disease by Three-Dimensional Transesophageal Echocardiography: Its Advantages and Limitations for Diagnosis

The purpose of this study was to evaluate the inner surface morphology of the aorta in different pathologies using three-dimensional transesophageal echocardiography (3D-TEE), and to clarify its feasibility and limitations for clinical application. Two-dimensional TEE was performed in 20 patients with aortic disease (12 aortic dissection, 4 aortic aneurysm, 4 aortic sclerosis) and 7 with normal aorta. Transverse view of the descending aorta was taken at each 2 mm interval by manually withdrawing the probe. Each image was recorded in VTR during one beat. Off-line data analysis was performed and 3D image was reconstructed using Lambert shading method. In 8 cases with DeBakey type III aortic dissection who had the entry or reentry and flow in the false lumen, 3D-TEE could demonstrate the irregularity on the shape of intimal tear and the wavy movement of flap, and clarify the accurate location of the intimal tear and the transverse and longitudinal extent of the dissecting flap in all cases. These coincided with the operating findings in 3 cases underwent surgical treatment. On the other hand, the image of inner surface area in 4 cases that the false lumen was filled with thrombus, could not be differentiated from a normal aorta. In cases with aortic aneurysm or atherosclerosis it was possible to visualize the spatial morphology of the aneurysm or plaque and determine its extension. However, nature of the plaque (soft or hard) and intramural thrombus (fresh or old), could not be estimated by the image of inner surface reconstruction. In conclusion, these results suggest that 3D-TEE has advantages in estimation of the surface morphology, spatial extent and actual location of aortic abnormalities and limitations in tissue characterization.

Spiral CT-angiography of the aorta

To determine whether the new technique of CT-angiography was accurate in displaying the complex anatomy of the aorta and its major branches. Seventeen patients with a variety of aortic pathology were examined. Using a spiral CT-scanner a volumetric scan was made during injection of 150 cc of i.v. contrast. Depending on the chosen CT technique, a body volume with a length ranging between 25-100 cm could be examined in one 50 second spiral scan. On the resulting transverse slices vascular lumina and extent of thrombus were studied. Subsequently, the transverse slices were reconstructed in the coronal or sagittal plane in order to appreciate the craniocaudal relations of the vascular anatomy. Finally, three-dimensional reconstructions were made of vascular lumina and thrombus. In aortic aneurysms the extent of the aneurysmal dilatation and of the adherent thrombus could be accurately located relative to the origins of renal and visceral branches proximally, and iliac bifurcation distally. In cases of severe elongation, dissection or complex anatomy, a detailed preoperative insight into the individual anatomy could be obtained. The two-dimensional axial and multiplanar reconstructions offered excellent anatomic detail. The three-dimensional reconstructions, being based on a considerable data reduction, offered an efficient means of providing an overall view of complex anatomic relations. The advantage of CT-angiography is that, based on a single spiral scan, the vascular structures in the examined body volume can be displayed in any desired plane using multiplanar reconstructions. Alternatively, three-dimensional renderings can be created. The combination of multiplanar reconstructions and three-dimensional reconstructions makes CT-angiography an accurate technique for displaying even the most complex aortic anatomy.

Photon spin and the paraxial wave equation

The spin of a circularly polarized wave in vacuo is clarified if one acknowledges the finite transverse extent of the wave. This is done self-consistently in the paraxial wave approximation.

Morphologic and functional analysis of myocardial status in pulmonary atresia with intact ventricular septum—an angiographic, histologic and morphometric study

SummaryWe studied 11 patients with pulmonary atresia and intact ventricular septum who died at ages ranging from one day to three years. All but two neonates died after surgery. Pre-surgical catheterization with left and right cineventriculography was performed in nine patients, and quantitative parameters were calculated. By histologic examination of transverse transmural sections, the incidence and extent of myocardial ischemia or infarction were determined, as well as the percentage area per field occupied by vessels, myocytes orientated longitudinally or transversely, interstitial space, and disarrayed fibers. Comparable sections were obtained from six normal neonates to constitute a control group. Myocardial ischemia or infarction were frequent complications. Morphometric analysis demonstrated a significant difference between the control group and the patients with regard to the percentage of myocytes (longitudinal and transverse), the percentage of area occupied by myocardial disarray, and the presence of fibrosis. The highest values for the proportion of disarray were seen in those patients with small right ventricles. The percentage of myocytes varied, but the highest degree of disarray always correlated with the lowest percentage of myocytes. The highest percentage value of left ventricular disarray was associated with the lowest ratio of left ventricular mass to end diastolic volume (inadequate hypertrophy). The lowest indices of contractility and left ventricular pump function were associated with myocytes less than 55% of normal. A linear correlation was found between the percentage area of fibrosis and the ratio of systolic pressure to end systolic volume in the left ventricle, arid between fibrosis and ejection fraction. Values for fibrosis exceeding 15% were associated with decreased functional indices. Disarray, therefore, seems to express a primary inability of myocardium to respond to anomalous overload with adequate hypertrophy and/or hyperplasia.

Observations of short large‐amplitude magnetic structures at a quasi‐parallel shock

We have conducted a detailed analysis of a set of events termed short large‐amplitude magnetic structures (SLAMS) observed at an encounter of the quasi‐parallel bow shock by the AMPTE UKS and IRM satellites. Both the satellite configuration and the solar wind conditions are favorable for the case study presented here. We have identified isolated SLAMS, surrounded by solar wind conditions, and embedded SLAMS, which lie within or form the boundary with regions of significant heating and deceleration. The duration, polarization, and other characteristics of SLAMS are all consistent with their growth directly out of the ULF wave field, including the common occurrence of an attached whistler as found in ULF shocklets. The plasma rest frame propagation speeds, where they can be determined, and two‐spacecraft time delays for all cases show that the SLAMS attempt to propagate upstream against the oncoming flow, but are convected back downstream. The speeds and delays vary systematically with SLAMS amplitude in the way anticipated from nonlinear wave theory, as do their polarization features. Inter‐SLAMS regions, and boundary regions with the solar wind, contain hot deflected ions of lesser density than within the SLAMS. The amplitude of the SLAMS requires an active growth mechanism. Following earlier inferences about the limited transverse extent of SLAMS, we highlight the importance of determining the thickness of the transition zone over which SLAMS grow and the bulk heating and deceleration is effected. From this case study it appears that, at least under some circumstances, the quasi‐parallel shock cannot be regarded as an undulating, cyclically re‐forming simply connected surface. Instead, the transition zone is better represented as a set of ULF waves, some of which grow to become SLAMS which gradually decelerate and merge to form the downstream state.

Quasi‐parallel shocks: A patchwork of three‐dimensional structures

Collisionless shocks at quasi‐parallel geometries, i.e., for which the average magnetic field direction upstream of the shock is close to the shock normal, reveal temporally varying quantities, a variety of boundary crossing and kinetic signatures, and magnetic structures, often convecting, of finite extent. These results can be put together by a framework in which the shock can be viewed as an extended region containing three‐dimensional Short Large Amplitude Magnetic Structures (SLAMS) which represent individual semi‐cycles of the ambient upstream low frequency waves associated with diffuse ions in the ULF foreshock. As SLAMS convect with the flow they grow to large amplitudes and entrain inter‐SLAMS regions to form an inhornogeneous downstream state. Their finite transverse extent is probably related to, and interacts with, ion beams, to produce a patchy transition zone which accounts for the variety of spacecraft signatures observed.

Quantum theory of self-phase modulation

The time-dependent Hartree approximation discussed by Lai Haus [ Phys. Rev. A40, 844 ( 1989)] is used to investigate the effects of self-phase modulation on a beam of finite transverse extent propagating through a Kerr nonlinear medium. For a thermal field the photon statistics can greatly alter the spatial frequency spectrum in comparison with that for a coherent field. This suggests the use of self-phase modulation as a probe of field photon statistics.