Narrow Slits Research Articles

A mesoscopic model of dissolution/disintegration of nanocrystalline metals via vacancy diffusion along grain boundaries

We propose a model describing the growth of a two-dimensional subsurface pore induced by vacancy supersaturation on the surface of a polycrystal. We demonstrate that the pore develops narrow slits propagating along the grain boundaries which may lead to disintegration of nanocrystalline metal by grain detachment. Analytic models describing initial and final (on the verge of grain detachment) stages of pore growth are proposed. The models’ predictions are in good agreement with the numerical simulation results.

Effects of narrow slits on frequency response of a microstrip square loop resonator and dual‐mode filter applications

AbstractIn this letter, the effect of narrow slits on resonance characteristics for a microstrip square loop resonator (SLR) with mitered bends is investigated and a new formula to calculate the resonance frequency of SLRs loaded inductively by means of slits is derived as a function of the number of slits.A novel dual‐mode SLR configuration performing a slow‐wave characteristic obtained by using narrow slits is proposed to use in design of microstrip dual‐mode bandpass filters. Also, a new perturbation technique based on the change of electrical lengths is presented for the excitation of two degenerated modes of these type resonators. Additional, two dual‐mode bandpass filters having linear phase and elliptical frequency characteristics have been designed, fabricated and tested to verify the proposed filter topology. Experimental results agree with simulated results. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:143–146, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27237

Functional Hyposplenism in Pediatric Chronic Graft-Versus-Host Disease

AbstractAbstract 4493 Introduction:Functional hyposplenism is a well-recognized complication of chronic graft versus host disease (cGVHD). Whether the hyposplenism in cGVHD is transient and if there is any association between the severity of cGVHD and degree of hyposplenism are not well understood. The pitted red cell count has been shown to be a simple and reliable biomarker of splenic function that correlates well to other tests such as quantitative Howell-Jolly bodies and 99mTc sulfur-colloid liver-spleen scans. It measures the ability of the splenic red pulp to pinch off intracellular vesicles, or pits, from red blood cells as they pass through narrow adjustable slits in an endothelial lining. Methods:We hypothesized that functional hyposplenism correlates with the severity of cGVHD in pediatric BMT patients. We performed a single-center, retrospective review of pediatric allogeneic bone marrow transplant (BMT) patients who had more then one pit count performed post-BMT and clinical diagnosis of cGVHD based on NIH consensus criteria. Results:We identified 9 pediatric BMT recipients (3 males, 6 females; average age at BMT = 9.6 years) that met our criteria. Indications for BMT were AML (2), ALL (1), biphenotypic acute leukemia (1), CML (2) and thalassemia (3). All 9 had functional hyposplenism with active cGVHD as determined by a pit count > 2%. We identified two distinct groups. In 7 of the 9 BMT recipients, there was a return to normal splenic function that lagged between 12 and 18 months after clinical improvement/resolution of cGVHD symptoms and successful weaning of immunosuppressive therapy. In the other 2 patients there was no correlation between abnormal pit count and cGVHD symptoms. Conclusions:Our single-centre retrospective cohort study provides evidence that the functional hyposplenism associated with cGVHD is not permanent but improvement in cGVHD symptoms and successful weaning of immunosuppressive therapy should not be used as indicators of return to normal splenic function and reasons to stop Penicillin prophylaxis. We propose that all patients post-BMT should have serial pit counts performed, as resolution of cGVHD clinical symptoms does not ensure normal splenic function. Disclosures:No relevant conflicts of interest to declare.

Reflection suppression and absorption enhancement of optical field at thin metal gratings with narrow slits

Optically thin metal gratings of high filling factor can support surface plasmon polariton modes at their horizontal metal boundaries and vertical cavity modes inside their slits. These modes are coupled through the metal stripes and the slits. This letter shows that the resonant interactions between the modes critically influence the optical field distribution near the grating and substantially enhance several phenomena such as low reflection, low transmission, and high absorption of the electromagnetic radiation. A high degree of energy confinement is obtained, especially when the energy is stored almost exclusively on the far side of the grating, away from the incident radiation. It is numerically shown that this phenomenon originates from the interaction of field modes with the collective motion of free electrons, as considered in the Drude model.

New Laser-Scan Exposure System for Delineating Precise Helical Patterns onto Sub-50-µm Wires

A new laser-scan exposure system for patterning onto fine wires and pipes with diameters as small as 40 µm was developed. New schemes for vertically holding specimens were adopted, and improved optics of imaging and in situ observation were used. In addition, specially contrived half-vacuum support guides were attached, and a short-wavelength violet laser with a wavelength of 408 nm was also attached. Because the laser beam spot was kept steady at a constant size by the improved half-vacuum support guide with triple narrow slits, patterns with homogeneous widths of approximately 20 µm were constantly delineated suppressing the width fluctuations to less than ±2 µm. In addition, owing to the short-wavelength laser, exposure time was greatly decreased to approximately 1/10 compared with the previous system. The new exposure system will be applicable to development of fine microcomponents such as microcoils useful for very fine probe pins of semiconductor device testers.

A model of interfacial cavitation induced by vacancy supersaturation on the surface

We considered the morphology and growth kinetics of a two-dimensional subsurface pore growing due to vacancy supersaturation on the surface of a polycrystal. We demonstrate that the pore develops narrow slits that propagate along the grain boundaries and lead to polycrystal disintegration by grain detachment.

Experimental demonstration of plasmonic Brewster angle extraordinary transmission through extreme subwavelength slit arrays in the microwave

We experimentally demonstrate the existence of a Brewster-like broadband extraordinary optical transmission band, in a very thick metal plate with an array of slits as narrow as $\ensuremath{\lambda}$/750 in the 8- to 40-GHz regime, by measuring the transmission from normal incidence to near grazing angles and mapping out the entire angular transmission spectrum. In the case of very narrow slits, an order of magnitude larger transmission is obtained at the Brewster angle when compared to the normal-incidence Fabry-P\'erot resonance transmission peaks. Full-wave numerical simulations are in excellent agreement with the measurements, paving the way for the observation of this phenomenon in the optical regime.

Properties of TM resonances on metallic slit gratings

Electromagnetic resonances on metallic slit gratings induced by TM polarized incident light have been investigated and physically interpreted. We have developed an electromagnetic model imposing surface impedance boundary conditions on the metallic grating surface from which we derive simple formulas explaining all physical properties of these resonances. It is demonstrated that Fabry-Perot (or cavity) resonances are generated by the zeroth slit mode yielding extraordinary transmission. For very narrow slits, the resonant H-field is squeezed to the slit walls and causes enhanced power losses. The excitation of surface plasmon polaritons (SPPs), however, is generated by two mode coupling. SPPs are linked to sharp absorption peaks and dips in transmittance. It is shown that these phenomena are primarily caused by the interaction of the electromagnetic fields with the finite conducting slit walls. These findings have been confirmed by measured transmittance data of gold gratings with periods of 0.5 μm, 1 μm, and 2 μm.

A potential role for differential contractility in early brain development and evolution

Differences in brain structure between species have long fascinated evolutionary biologists. Understanding how these differences arise requires knowing how they are generated in the embryo. Growing evidence in the field of evolutionary developmental biology (evo-devo) suggests that morphological differences between species result largely from changes in the spatiotemporal regulation of gene expression during development. Corresponding changes in functional cellular behaviors (morphogenetic mechanisms) are only beginning to be explored, however. Here we show that spatiotemporal patterns of tissue contractility are sufficient to explain differences in morphology of the early embryonic brain between disparate species. We found that enhancing cytoskeletal contraction in the embryonic chick brain with calyculin A alters the distribution of contractile proteins on the apical side of the neuroepithelium and changes relatively round cross-sections of the tubular brain into shapes resembling triangles, diamonds, and narrow slits. These perturbed shapes, as well as overall brain morphology, are remarkably similar to those of corresponding sections normally found in species such as zebrafish and Xenopus laevis (frog). Tissue staining revealed relatively strong concentration of F-actin at vertices of hyper-contracted cross-sections, and a finite element model shows that local contraction in these regions can convert circular sections into the observed shapes. Another model suggests that these variations in contractility depend on the initial geometry of the brain tube, as localized contraction may be needed to open the initially closed lumen in normal zebrafish and Xenopus brains, whereas this contractile machinery is not necessary in chick brains, which are already open when first created. We conclude that interspecies differences in cytoskeletal contraction may play a larger role in generating differences in morphology, and at much earlier developmental stages, in the brain than previously appreciated. This study is a step toward uncovering the underlying morphomechanical mechanisms that regulate how neural phenotypic differences arise between species.

Simulation of Angular Distribution of Molecular Flux at the Exit of Narrow Tubes and Slits

In order to develop a gas-sheet target, the angular distribution of molecular flux at the exit of narrow tubes and slits was simulated by employing the Monte Carlo method. In the case of the longer tubes, the greater part of the flux is collimated near the polar angle. However, when the ratio of length to diameter, L/d (L: length, d: diameter), is greater than 10, angular distribution is almost independent of the L/d value. Even at the L/d value of 100, the fraction of outgoing molecules with polar angles less than 0.01 rad is less 0.5%. The molecules emitted from the slit can be shaped into a sheet. To do so, the following two conditions need to be satisfied: L≫b and a≫b. The letters a, b, and L represent the lengths of the long and short sides, and the depth of the slit, respectively. With the parameter set of L:a:b=100:50:0.1, the fraction of outgoing molecules collimated within the azimuth of 0.01 rad becomes 25% of all molecules.

Wavelike deformation traveling on a carbon nanotube

The propagation of wavelike ripples on a carbon nanotube (CNT) induced by the radial impact of a C(60) molecule is investigated by molecular dynamics simulations. The ripples start at the impact point and spreads through the tube, accompanied by energy transfer. The ripples would effectively reduce the local energy concentration around the impact point. The propagation of ripples is clearly affected by the diameter but is independent of the chirality of the CNT. Noticeable diffraction occurs when the deformation ripples encounter obstacles or narrow slits, which indicates that the propagation of ripples can be used to detect defects in the CNT. This work provides new and exciting possibilities for CNTs to serve as energy buffers, sensors and new nanoelectromechanical devices.

Localized and collective magnetoplasmon excitations in AlGaN/GaN-based grating-gate terahertz modulators

Magnetotransport and magnetooptics investigations of plasmon excitations in large-area grating-gate terahertz modulators based on AlGaN/GaN high-electron-mobility transistors with different grating-gate duty cycle are reported. We demonstrate that the effect of the gate potential on the ungated region extends beyond the conventional fringing effect distance, ranging over 250–350 nm instead of expected 26–30 nm. This phenomenon enables excitation of the localized gated magnetoplasmon modes only if the inter-finger spacing in the grating gate exceeds 350 nm. For narrower slits, only the collective gated magnetoplasmon modes extending over the entire period of the structure can be excited.

Finite element modelling of acoustic field inside small components: application to an annular slit terminated by an aperture in an infinite screen

Investigating accurately the acoustic behaviour of small fluid-filled cavities and ducts and their association is a problem of persistent importance, because nowadays both experimental investigations and theoretical modelling must provide results of increasingly higher precision. The motivation here is provided mainly by the acoustic measurement tools used for both the calibration of microphones and the artificial ear (IEC 60318-1). Both improved analytical models of small acoustic components (small tubes and slits), which account for the effects of the viscous and thermal boundary layers accurately in the frequency range of interest (20 Hz to 20 kHz), and experimental characterization of their input impedances (with a relative uncertainty of the order of magnitude of 10−2) have been proposed recently (Rodrigues et al 2008 J. Sound Vib. 315 890–910). Existing analytical procedures for coupled components suffer from strong approximations at the interfaces between narrow tubes and slits or other elements as well as the open space. A dedicated numerical model can be used in order to investigate accurately the acoustic field at these interfaces. The numerical model presented in the paper relies on a suitable linear exact formulation, based upon two coupled equations involving particle velocity and temperature variation (Joly 2010 Acta Acust. United Acust. 96 102–14) and utilizes an adaptive anisotropic meshing technique to model correctly the strong variations which occur around the geometrical discontinuities and inside the boundary layers. Application to a 2D axisymmetrical device (annular slit ending in an aperture in an infinite screen) is considered to present the ability of the method. Acoustic pressure, temperature variation and particle velocity distributions inside and around the end of the slit are depicted, and the input acoustic admittance of the slit obtained numerically is compared with both experimental and analytical results available.

Enhanced Reflection in One-Dimensional Mostly-Hollow Metallic Gratings at Terahertz Frequencies

Enhanced transmission through metallic gratings with narrow slits is a well-known phenomenon for TM polarized waves at optical and microwave frequencies. A similar though fundamentally different phenomenon, i.e., enhanced reflection at terahertz frequencies, is reported here for the geometrical complement of the structure with narrow slits. The latter phenomenon cannot be related to the former by Babinet's principle, as their origin is quite different, and both are observed for the same polarization. This phenomenon is explored by studying the field profiles within the grating, and is attributed to the presence of TM cavity modes at specific frequencies. A simple formula is given to anticipate the frequencies at which the anomalies appear. The accuracy of this formula is verified by using a rigorous numerical approach.

A Novel Compact Electromagnetic Bandgap Structure in Power Plane for Wideband Noise Suppression and Low Radiation

A compact reduced unit cell size electromagnetic bandgap (EBG) power plane, realized with a combination of alternating impedance EBG and multiple narrow slits, is presented. By concatenating 2 × 2 high-frequency unit cells, a virtual low-frequency EBG unit cell is synthesized without changing the overall dimensions. In this configuration, the basic slit in the high-frequency unit cell remained same, and an additional slit with longer dimensions is added in parallel to the basic slit by synthesizing a larger low-frequency unit cell. EBG is characterized for its dispersion diagram, noise suppression, signal integrity, and electromagnetic radiation. Fabricated EBG exhibits a bandgap from 0.9 to 3.5 GHz with isolation better than -40 dB over the band. Radiated emission of the new EBG is small with an average value of 35 dB·uV/m. Compact EBG also exhibits low impedance, which is less than 1 Ω over the stopband. Eye patterns are generated to analyze signal integrity issues when the data lines are referenced over the solid ground plane and EBG plane. The degradation of the maximum eye opening and the maximum eye width for the proposed EBG power plane at 2 Gb/s data rate is about 17.8% and 1%, respectively, with reference to the equivalent board with solid power plane.

Multi-Slit Electromagnetic Bandgap Power Plane for Wideband Noise Suppression

A compact reduced size electromagnetic bandgap (EBG) structure with multiple narrow slits unitcell is presented. The new EBG structure is realized with a combination of alternating impedance EBG and multiple narrow slits in power plane. By concatenating 2 × 2 high frequency unitcells, a virtual low frequency EBG unitcell is created without changing the overall dimensions. In this configuration, the basic slit in the high frequency unitcell remained same and an additional Z-slit is added in parallel to the basic slit with larger dimensions by synthesizing a larger unitcell. This new configuration provides low onset frequency and wideband noise suppression with small unitcell dimensions. Measured and simulated results show noise suppression and isolation over 50 dB in most of the stop-band (0.7-3.5 GHz) and also exhibit low impedance, which is less than 1 Ω over the stop-band. Eye patterns are generated for analyzing signal integrity referenced to the solid power/ground plane and EBG plane. Maximum eye opening (MEO) and the maximum eye width (MEW) analyzed for the signal on EBG reference plane are presented and compared. The degradation of the MEO and MEW for the proposed EBG board is about 16.2 and 1%, respectively, with reference to the equivalent board with solid power plane.

Magnetic imaging by x-ray holography using extended references

We demonstrate magnetic lensless imaging by Fourier transform holography using extended references. A narrow slit milled through an opaque gold mask is used as a holographic reference and magnetic contrast is obtained by x-ray magnetic circular dichroism. We present images of magnetic domains in a Co/Pt multilayer thin film with perpendicular magnetic anisotropy. This technique holds advantages over standard Fourier transform holography, where small holes are used to define the reference beam. An increased intensity through the extended reference reduces the counting time to record the farfield diffraction pattern. Additionally it was found that manufacturing narrow slits is less technologically demanding than the same procedure for holes. We achieve a spatial resolution of ∼30 nm, which was found to be limited by the sample period of the chosen experimental setup.

Guided mode resonance in subwavelength metallodielectric free-standing grating for bandpass filtering

We present the experimental study of a free-standing metallic guided-mode resonant structure, for bandpass filtering applications in the mid-IR wavelength range. Structure consists of a subwavelength gold grating with narrow slits deposited on a silicon nitride membrane. High optical transmission is measured with up to 78% transmission at resonance. Angularly resolved spectra are presented revealing Fano-type resonance.

Raman Spectroscopy Using a Spatial Heterodyne Spectrometer: Proof of Concept

The use of a spatial heterodyne interferometer-based spectrometer (SHS) for Raman spectroscopy is described. The motivation for this work is to develop a small, rugged, high-resolution ultraviolet (UV) Raman spectrometer that is compatible with pulsed laser sources and that is suitable for planetary space missions. UV Raman is a particular technical challenge for space applications because dispersive (grating) approaches require large spectrographs and very narrow slits to achieve the spectral resolution required to maximize the potential of Raman spectroscopy. The heterodyne approach of the SHS has only a weak coupling of resolution and throughput, so a high-resolution UV SHS can both be small and employ a wide slit to maximize throughput. The SHS measures all optical path differences in its interferogram simultaneously with a detector array, so the technique is compatible with gated detection using pulsed lasers, important to reject ambient background and mitigate fluorescence (already low in the UV) that might be encountered on a planetary surface where samples are uncontrolled. The SHS has no moving parts, and as the spectrum is heterodyned around the laser wavelength, it is particularly suitable for Raman measurements. In this preliminary report we demonstrate the ability to measure visible wavelength Raman spectra of liquid and solid materials using an SHS Raman spectrometer and a visible laser. Spectral resolution and bandpass are also discussed. Separation of anti-Stokes and Stokes Raman bands is demonstrated using two different approaches. Finally spectral bandpass doubling is demonstrated by forming an interference pattern in both directions on the ICCD detector followed by analysis using a two-dimensional Fourier transform.

All-optical switching at the Fano resonances in subwavelength gratings with very narrow slits

We theoretically discuss all-optical switching at the Fano resonances of subwavelength gratings made of a chalcogenide glass (As(2)S(3)). Particular attention is devoted to the case in which the grating possesses extremely narrow slits (channels ranging from a∼10 nm to a∼40 nm). The remarkable local field enhancement available in these situations conspires to yield low-threshold switching intensities (~50 MW/cm(2)) at telecommunication wavelengths for extremely thin (d∼200 nm) gratings when a realistic value of the As(2)S(3) cubic nonlinearity is used.