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A slit structure consisted of two bending graphene membranes is built as a nano check valve theoretically. Molecular dynamics simulations are used to investigate the opening and closing of this check valve. The backflow through the valve are also studied. The results show that the check valve can maintain the unidirectional flow of fluid and prevent backflow within the appropriate pressure range. Specifically, the opening and closing pressure of the valve are 148.2 and 24.6 MPa, respectively. The maximum working pressure of the check valve should be lower than 197.6 MPa. Moreover, the water passing rate is larger at a higher pressure due to the larger slit width and water flux. This check valve is expected to have many potential applications in the nanofluidic field.

In this paper, investigation on fiber laser cutting of CFRP was carried out through establishing a multi-physical finite element model and cutting experiment. A multi-physical field model of laser cutting of CFRP was established. Experiments on 1 kW fiber laser cutting of 1 mm CFRP was performed. The relationship between cutting quality (slit width, notch taper, and HAZ width) and laser process parameters such as laser power and cutting speed was investigated. The results show that the transfer of laser energy in CFRP is mainly along the direction of fiber laying, and the heat transfer speed in carbon fiber is much faster than that in resin. The width of the slit, HAZ and the notch taper all increase with the increasing of laser power. However, the width of slit and HAZ decrease as the cutting speed increase and the notch taper increased first and then decreased. When the laser power is 150 W and the cutting speed is 1 m/min, the cutting quality is better.

We study, in this paper, the physical properties of water confined between two parallel graphene plates with different slit widths to understand the effects of confinement on the water structure and how bulk properties are reached as the water layer thickens. It was found that the microscopic structures of the interfacial liquid layer close to graphene vary with the slit width. Water tends to locate at the center of the six-membered ring of graphene planes to form triangular patterns, as found by others. The narrower the slit width is, the more pronounced this pattern is, except for the slit width of 9.5 A, for which a well-defined two-layer structure of water forms. On the other hand, squared structures can be clearly seen in single snapshots at small (6.5 A and 7.5 A) but not large slit widths. Even at small slit widths, the square-like geometry is observed only when an average is taken for a short trajectory, and averaging over a long time yields a triangular pattern dictated by the graphene geometry. We estimate the length of time needed to observe two patterns, respectively. We also used the two-phase thermodynamic model to study the variation of entropy of confined water and found that at 8.5 A, the entropy of confined water is larger than that of bulk water. The rotational entropy of confined water is higher than that of bulk water for all slit widths due to the reduction of the hydrogen bond in the confined space.

The Beijing Faint Object Spectrograph and Camera (BFOSC) is one of the most important instruments of the 2.16-m telescope of the Xinglong Observatory. Every year there are ~ 20 SCI-papers published based on the observational data of this telescope. In this work, we have systemically measured the total efficiency of the BFOSC of the 2.16-m reflector, based on the observations of two ESO flux standard stars. We have obtained the total efficiencies of the BFOSC instrument of different grisms with various slit widths in almost all ranges, and analysed the factors which effect the efficiency of telescope and spectrograph. For the astronomical observers, the result will be useful for them to select a suitable slit width, depending on their scientific goals and weather conditions during the observation; For the technicians, the result will help them systemically find out the real efficiency of telescope and spectrograph, and further to improve the total efficiency and observing capacity of the telescope technically., 13 pages, 11 figures, 4 tables, accepted for publication in RAA

We study the conformational behavior of spherical polyelectrolyte brushes in the presence of monovalent and trivalent counterions in a confined environment. The confinement is exerted by two parallel walls on the brushes. The enhancement of the confinement induces the extension of grafted chains. For the monovalent case, the increase of the charge fraction leads to extended brush conformation for different slit width (distance between two walls) but collapsed brush in the presence of trivalent counterions is observed. The confinement does not affect electrostatic correlation between trivalent counterions and charged monomers. However, it was found that narrow slit width contributes to stronger electrostatic correlation for the monovalent case. This is because more monovalent counterions are inside the brush at strong confinement, but almost all trivalent counterions are trapped into the brush independently of the slit width. The diffusion of counterions under the confinement is related to the electrostatic correlation. Our simulations also reveal that the brush thickness depends on the slit width nonlinearly.

Theoretical simulation and experiments based on a prism beam expander and an echelle grating are conducted to study the dependence of linewidth and pulse energy on incidence angle and slit width. With a larger prism incident angle or narrower slit width, the linewidth becomes narrower while the laser pulse energy becomes lower. However, the pulse energy can be improved by optimally designing the prism beam expander. In addition, a subpicometer linewidth ArF laser is obtained with a double-prism beam expander and an echelle grating.

Microarray technology has emerged as a major player in the parallel detection of biomolecules, but it still suffers from fundamental technical problems. Theoretical analysis of the printing process is crucial to achieve high quality microarrays. In this paper, modelling and hydrostatic analysis of contact printing microarrays by quill pins are presented. First, a complete contact printing process was modelled and divided into four stages: sample dipping, sample transferring, contact printing and spot spreading. Then, the hydrostatics mathematical model of each stage was developed. Based on the model analysis, the printing stability and continuity criteria and key parameters were described quantitatively. The results show that the slit width in the pin tip, the slit inclination and contact angle of quill pins have dominant effects on the stable and continual printing process. Finally, the quill pins were optimally designed and manufactured. A robotic microarray fabrication system using the quill pins was successfully developed and used to produce protein microarrays for biological applications.

Miniaturisation of metallic structures has become a prime issue and to meet high demand, modern fabricators extensively use different micro machining techniques. Wire electrochemical machining (wire ECM) is such a process of removing excess material electrochemically. However, the process is still new and further research is needed. Hence, the present work aims in developing suitable wire ECM setup to find out the influence of wire feed rate at varying voltage settings on corresponding width of the generated microslits. For this, experimentations have been carried out with 50 μm dia tungsten wire and machined micro features have been carefully observed under optical microscope. Additionally, the experimental results have been represented graphically where the minimum average width of the microslit is found to be 83.117 μm with an aspect ratio of 1.2. Moreover, complex microfeature with varying width has been fabricated by changing corresponding feed values in a single run.

Purpose To evaluate a custom-made ocular fluorometer for detection of intensity of light scatter (ILS) from the anterior chamber (A/C) as an objective measure of aqueous flare. Methods The fluorometer, equipped with a lock-in amplifier, was employed in the scatter mode to detect ILS from A/C. Measurements were performed with two illumination slit widths of 0.5 and 0.25 mm. The axial resolution at these slit widths were 80 and 200 μm, respectively. Healthy and pseudophakic eyes, with grade 0 Standardization of Uveitis Nomenclature (SUN) score, were employed as control subjects. ILS was also recorded in a cohort of patients who had undergone phacoemulsification and showed grades 1+ or 2+ on postoperative days 1 and 4. Results The inter- and intraobserver variabilities in the measurement of ILS were not significant. In cataract patients, ILS was significantly higher on postoperative day 1 relative to healthy eyes. By day 4, ILS decreased significantly and was only marginally different from ILS in quiet pseudophakic eyes or healthy eyes. Eyes with higher SUN scores showed proportionately increased ILS. The receiver-operator characteristic analysis indicated no advantage in using the smaller slit width in discriminating ILS at different SUN scores although it provided higher axial resolution. Conclusions The lock-in-based spot fluorometer is reliable for measurement of ILS with high precision and accuracy.The measured ILS correlates linearly with SUN scores and can be used to provide a higher granularity for recording aqueous flare. Translational relevance The instrument can be used in the clinical management of uveitis and drug development toward uveitis.

We provide measurements of Young’s double-slit experiment using a partially-coherent light source consisting of a helium-neon laser incident on a rotating piece of white paper. The data allow a quantitative comparison with both the standard theory that does not account for the width of the slits, and a full, analytic model that does. The data agree much more favorably with the full calculation.

This study investigates the influence of slit positions on the microclimate temperature/humidity of garments. To design the slits, a market survey was performed to indicate the method to apply the slits, in addition to a literature survey about muscles and body surface variation through body movements. Based on the survey, three positions of slits were selected, shoulder slit, lowback slit, and midback slit, a slit width of 1cm and length to 30cm was used. The results showed that microclimate temperatures/humidity on the back according to the slit positions were in the order of, lowback, midback, and the shoulder. The lowback slit showed the highest effect on the temperature/humidity of a front trunk. Lowback slits affected on localized areas of the glutaeus maximus, erector spinae, and latissimus dorsi. Midback slits affected the back muscle and deltoid. Shoulder slits showed a more significant effect on the localized area of the deltoid versus other localized areas. In the subjective sensations, the lowback slit was cooler, dryer, and more comfortable than the other slits. For the subjective sensations by fabric characteristics, the slit positions correlated at |r| and were significant at p

We present a procedure for measuring slit width and separation in single- and double-slit diffraction experiments. Intensity spectra of diffracted laser light are measured with an optical sensor (PIN diode). Slit widths and separations are extracted by fitting to the measured spectra. We present a simple fitting procedure to account for the integration (averaging) of light across the finite sensor aperture. This experiment provides students with a quantitative, in-depth verification of diffraction theory, as well as hands-on experience in sophisticated fitting methods.

We theoretically demonstrate the formation of different kinds of two-dimensional split-ring arrays in both triangular and square lattices by one-step holographic interference. The slit width of the split-ring can be adjusted by proper polarization configurations. The dimension of the rings can be adjusted easily by using different wavelengths for interference, so the resonant frequency of the split-rings can be obtained in a wide range. Our theory is also proved in experiment. Our work would extend the application of holographic lithography to the fabrication of magnetic metamaterials., It will be very interesting to the nanofabrication, optical interference lithography and metamaterial communities

We present a new technique to analyze the absorption efficiency of the active medium for a LD side-pumped Nd:YAG laser. A detailed ray trace has been carried out to evaluate the route of the pump LD-rays propagating inside the diffusing chamber. The method, named the infinite convergence approach, is used to determine the total absorbed power of a Nd:YAG rod when random reflection takes place at the inner surface of the reflector wall. By reason of losses caused by slits milled the reflector wall, there is an optimum slit width corresponding to the maximum absorption efficiency. It has been theoretically determined that the absorption efficiency can be summarized by a convergent result for the infinite energy transfer process inside the diffusing chamber. The method is applicable to the cavity design for any LD side-pumped solid-state lasers.

An attempt has been made to analyze the methods to improve the electromagnetic properties of a solid-rotor high speed induction motor. The slitting patterns of the solid rotor are examined. It is shown how the slitting parameters affect the produced torque. The paper considered the effect of variation of slit depth and slit width for two materials with different electrical properties, on the performance of 180 kW, 170 Hz 3-phase induction motor using Flux-2D Maxwell software package from ANSYS. It is found that deeper rotor slit gives better and higher starting torqueas well as maximum torque. Also a comparative study with a double cage rotor slot is presented which leads to further improvement of running performance of the high speed induction motor.

The final status of the optical design of the Russian–German soft-X-ray beamline at BESSY II is presented. Ray-tracing calculations provide the optimized parameters of the optical layout based on a Petersen-type plane-grating monochromator that operates with collimated light. Resolving power up to 25,000 and photon flux up to 3×10 10 photons/s/100 mA with a slit width of 20 μm will be available for spectroscopic experiments.

A previously developed method (Hag and Schatzki 1993) for detecting pits in red tart pitted canned cherries was expanded to detect pit fragments as well. fie cherries were pulped in a modified kitchen blender and poured into a slit sieve designed with an adjustable slit width to let the cherry pulp wash through while retaining the pits and fragments. Some further fragmentation of pit fragments occurred during blending (3-5.5%), but can be corrected for. With an optimized slit width of 1.5 mm, 79% offragments were caught by the sieve and thus detected, independent of fragment length. Passage of fragments followed a binomial distribution. fiis method, while not an on-line one, uses exceedingly simple and inexpensive equipment and is ideally suited for field testing.

There are a number of interesting articles1 that have discussed qualitative, quantitative, and other aspects of thermal expansion. A method to determine linear coefficient of thermal expansion using readily available materials is presented here. The design of the apparatus for this method allows for the width of a single slit to increase by the same amount as the thermal expansion of a length of a strip or a rod of a material. A laser is used to obtain a diffraction pattern for the single slit. The increase in the slit width, hence the linear expansion, can be measured by analyzing the diffraction pattern. The value of the linear coefficient of thermal expansion of the material can then be calculated.

This paper presents the Espresso Anamorphic pupil Slicer (APSU) implementation. For ESPRESSO that will be installed on ESO’s Very Large Telescope (VLT). In this work we will present the design and trade off for the pupil slicing system introduced in order to increase the resolving power, effectively decreasing slit width. It’s based onto simplified optical component that introduce large anamorphism while keeping low aberrations by means of cylindrical optics. We describe here the trade off between slicing through two adjacent squared doublets and two achromatic prisms. Preliminary integration and procurement is also discussed here.

After studying the factors of how, the slit width of a slitted bluff-body (SBB) burner influences the cold state flow field, the hot state temperature and gas concentration fields. the following important conclusions are obtained: the slit width influences not only flow characteristics behind the slitted bluff-body such as the size and reflux rate of the recirculation region. but also the quantity of pulverized coal jetting into it. To use it in an industrial plant, the optimal value of slit width is determined as about 10 percents of the width of the bluff-body (BB).

16th Conference of Novel Optical Systems Design and Optimization, August 26-28, 2013, San Diego, CA, USA, Series: Proceedings of SPIE

An array of ring-shaped holes is prepared from silver thin films using electron beam lithography. The optimal conditions for high performance as a surface-enhanced Raman scattering (SERS) substrate are investigated. Either the diameter of the hole (0.5, 1.0, 2.0, 3.0 and 4.0 µm) or the slit width (200, 300, 400, 500 and 600 nm) is varied. 4-Aminothiophenol (ATP) adsorbed on the structures as a self-assembled monolayer (SAM) is used as probe to evaluate the SERS performance of the generated structures. It is found that there is an optimal configuration for ring-shaped holes with a 3.0-µm diameter and 200-nm slit width. The SERS activity on this optimal lens configuration is found to be 13 times greater than that of the activity on the silver thin film. An array of these structures at this optimal configuration can easily be constructed and used in a range of SERS-based sensing applications. An array of ring-shaped holes is prepared from silver thin films using electron beam lithography. The optimal conditions for high performance as a surface-enhanced Raman scattering (SERS) substrate are investigated. It is found that there is an optimal configuration for ring-shaped holes with a 3.0-µm diameter and 200-nm slit with. The SERS activity on this optimal lens configuration is found to be 13 times greater than that of the activity on the silver thin film. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wavelength calibration is important for monochromator and spectrograph before accurate application. In the case of a Czerny-Turner double monochromator, work have been down to find out the relationship between slit widths and wavelength error. We do wavelength calibration in different widths of entrance and exit slits, then get wavelength error. The result shows that different widths of entrance slit and exit slit lead to different wavelength error, and wavelength error can be presented as a function of wavelength and slit widths through curve fitting. Thus, correction can be done by solving this function before accurate measurement.

Bandwidth is an important specification for monochromator and spectrograph. It varies with different slit widths and wavelengths. In actual spectral measurement, it is usually need to know the bandwidth. In the case of a Czerny-Turner double monochromator, we measured its bandwidth in finite different wavelengths as well as slit widths. Bandwidth can be represented as a function of wavelength and slit width. After the experiment, we get bandwidth in some discrete wavelengths and slit widths, bandwidth in other wavelength and slit width can be computed through mathematical process of the data that already acquired.

The silicate layers of montmorillonite clay were pillared with SiO2–TiO2 sol particles. Although only the SiO2 sols were negatively charged, the SiO2–TiO2 mixed oxide sols were positively charged and could be ion-exchanged with the interlayer cations of montmorillonite. The resulting pillared clays had a basal spacing expanded to more than 40 A; the spacing was maintained during calcination up to 773 K. The adsorption properties of the calcined samples were studied for nitrogen as well as organic vapors. A structural model for the arrangement of the intercalated sol particles is proposed in which small SiO2–TiO2 sol particles are packed between the silicate layers. Micropores with a slit width of 10–12 A are formed in the interstices between the sol particles and the silicate layers.

We have proposed an integrated Fresnel lens with multiple slits in a Si slab waveguide. The slit width and the slit spacing were optimized and the integrated lens had a reflective loss of 0.38 dB.

An analysis of distortions in holographic stereograms is presented. Particular attention is paid to the effects of viewing position and the slit width on the shape of reconstructed images. The cause and effects of anamorphic distortion and image quantization are dealt with separately and guidlines for minimizing the latter are given.

The formula g = wd2/[4pia(d+t)h] sin2thetas is derived for the sensitivity of a slit-slat collimator. Both Monte Carlo and experimental data confirm the expected dependence of g on the parameters, especially the distance from the plane of the slit h and the off-axis angle thetas. To refine agreement, a formula for the sensitivity-equivalent slit width is derived to account for slit penetration. At least at low energy its predictions agree well with Monte Carlo data and its use improves agreement with experimental data.

A constant‐deviation constant‐length spherical grating monochromator was constructed at the bending‐magnet beamline 8B1 of the UVSOR. The monochromator has a simple scanning mechanism with a fixed position of the entrance and exit slits, as well as fixed directions of incident and exit photon beams. The monochromator was designed to cover the photon energy of 31–620 eV with three interchangeable laminar gratings (1080 lines/mm: R=15 m, 540 lines/mm: R=15 m, 360 lines/mm: R=7.5 m). All gratings are original gratings fabricated on synthetic quartz substrates and coated with Au. The resolving power evaluated by ray tracing at the lowest energy of each grating with 10 μm slit width is ∼4400 for two high energy gratings and ∼7000 for a low energy grating. In the preliminary performance check, it was found that the output spectrum of the monochromator with G1 grating extends up to 870 eV with resolving power of ∼4000 at 400 eV with 10 μm slits.

The UIST instrument is a 1-5μm Imager Spectrometer for the UKIRT telescope. The instrument has a high spatial resolution, and is designed to critically sample image sizes of 0.24arcsec. The instrument weighs 750kg and measures approximately 1100x1000x700mm. The flexure specification for the instrument is to maintain the image at the slit within 10% of the narrowest slit width, which is 44μm wide. However combined flexure of the instrument and its supporting structure is expected to be many times more than this. To meet the UIST flexure requirements we propose use of an instrument specific component in the telescope pointing model, to correct for repeatable flexure. Two designs for mounting regimes are presented, together with flexure test results and a discussion of the use of a simple pointing correction. The first, flexible, truss design did not meet requirements and was replaced with a rigid truss system. The paper describes some lessons learned during the development of the UIST mounting scheme, which can be applied in other instrument designs.

The remarkable performance of the micromechanical slit device makes it possible to equip diode-array detectors with adjustable entrance slits. The device combines the required optical functions, i.e., slit and shutter, in a simple, reliable and compact component. The slit width is directly controlled by the microprocessor of the instrument and can be set as method parameter. It is used in the HP1100 Series HPLC Diode-Array Detector.

The silicate layers of montmorillonite clay were pillared with SiO2–TiO2 sol particles. Although only the SiO2 sols were negatively charged, the SiO2–TiO2 mixed oxide sols were positively charged and could be ion-exchanged with the interlayer cations of montmorillonite. The resulting pillared clays had a basal spacing expanded to more than 40 A; the spacing was maintained during calcination up to 773 K. The adsorption properties of the calcined samples were studied for nitrogen as well as organic vapors. A structural model for the arrangement of the intercalated sol particles is proposed in which small SiO2–TiO2 sol particles are packed between the silicate layers. Micropores with a slit width of 10–12 A are formed in the interstices between the sol particles and the silicate layers.

This article reports on the separation and determination of Cr(III) and Cr(VI) with cation-exchange chromatography and flame atomic absorption spectroscopy. A sample containing the two ions is added to a column containing a cation-exchange resin; the Cr(VI) ions are not retained by the resin and are collected in the effluent. The Cr(III) ions are retained by the resin and eluted with an HCl solution. The separated ions are aspirated into an air/acetylene flame and the absorbance measurements are made at λ = 357.9 nm and 0.2-nm slit width. The experiment has been implemented in a quantitative methods of analysis course. The results of the analysis of synthetic water samples obtained by students majoring in various areas of science are presented. The data showed that 58% of the Cr(VI) and 39% of the Cr(III) values had relative errors in the range of ±5%. The evaluation of the precision of the student results revealed that 48% of the Cr(III) and 81% of the Cr(VI) reported values had RSD ≤ 4%. This experiment...

A technique for calibrating slit width for straight spectrometer slits based on the diffraction of laser radiation is described. Related slit properties and calibration apparatus are discussed.

The original papers of Walsh and L'vov anticipated that atomic absorption spectroscopy would be capable of absolute, or standardless analyses. This paper shows that the modern graphite furnace technique provides standardless analyses in varied and complex matrices within about 10–20% accuracy. Some of the conditions that control the remaining variability are the atomization temperature and spectroscopic variables such as spectral slit width and lamp current. Nevertheless, characteristic mass data collected from nominally similar conditions in different laboratories for many elements show a spread of about ±15%, in spite of all the variables. A group of materials was analysed for several elements using only characteristic mass data for calibration and the results were compared with previous analyses of these materials. The results supported the 10–20% accuracy of this approach

The stochastic method of analysis of band spectra of asymmetric rotors involves the calculation of line strengths and positions for successive estimates of six molecular constants, until the calculated intensities at all wave‐lengths agree satisfactorily with the observed. This paper shows that these extensive calculations, as based on tables previously published, are well adapted to standard punched‐card equipment. In addition to the above calculations, it is possible to construct the appearance of the rotational structure for various values of slit width. The procedure is carried through for H2S with some approximate constants. Very satisfactory representations of observed spectra are obtained for completely resolved spectra, as in the photographic region; for slit width 1 and 2 cm−1, as in the near infra‐red; for slit width 10 cm−1, as in poorly resolved infra‐red spectra.

Synopsis The measurements of Winkel, Broese van Groenou and Gorter on the heat conduction in liquid helium II have been extended to lower temperatures. At 1.1 and 1.2°K the heat conduction still appears to be proportional to the cube of the slit width h in not too narrow slits. The viscosity computed from these data thus appears to have physical significance. There is a tendency for the viscosity to rise at the lowest temperatures but this effect is not so pronounced as has been found in oscillating disc and rotating viscometer experiments. No Knudsen or Klemens effects have been found.

A spectrochemical procedure to determine the ratio of the concentration of argon in a sample slightly different from air to the concentration of argon in air was developed using an electrodeless discharge tube and a 22-foot direct-reading optical spectrometer. A precision of ±0.43% at the 95% confidence level was obtained for a single determination made in 1 minute. A method of relative precisions to obtain optimum adjustments of the equipment is described. This method was used to determine the optimum discharge tube pressure and the optimum entrance slit width.

Flame photometric determination of 0.001% Na in primary standard potassium iodate by applying the “ Linear Extraporation Method ” is reported.By reason of the working curve of Na in 1% KIO3 solution being linear up to 1 p.p.m. Na content and its background flat, the above method becomes applicable.Under the condition of oxygen pressure 13 psi, acetylene pressure 3.5 psi, slit width 0.02 mm, and by using Beckman DU flame photometer with photomultiplier, 0.001% Na in KIO3 was determined with good precision. If sufficient care is taken to prevent the intrusion of Na, this method is more simple and more rapid as compared with the usual method.

Synopsis Further experiments are carried out on the flow of liquid helium II in an annular flat slit, with a length of 0.134 cm. The slit width varied between 0.4–6 microns. The frictional force F, defined as the difference between the observed and theoretical fountain effect, was studied in its dependence on the (relative) velocity v. It was found to vary with a power of this velocity, which in most cases was not very different from three. Comparison of the absolute values of the frictional forces with those obtained earlier in a longer slit (0.434 cm) indicates that the forces are roughly proportional to the slit length. This result suggests that the friction phenomena do occur in the whole slit and not only at the (narrowest) entrance.

The experimental determination of the resolving power of infrared spectrometers by means of sharp absorption lines is discussed. Under certain conditions the convolution of the true line profile with the monochromator function approximates completely to the latter, from where the spectral slit width can be obtained immediately. Some suitable lines in the absorption spectra of small gas molecules are suggested for calibration purposes.

The best experimental conditions for zinc determinations by atomic absorption spectrophotometry, air pressure, slit width and concentration limits have been established. The precision of the method is calculated on the basis of error calculus of absorption measurements. If solutions containing 30–120 ppm of Zn 2+ are measured, the relative errors are lower than ±0.5%. Interferences of anions and cations have been investigated, and found in most cases to be negligible.

This paper describes simple methods for determining spectral bandwidth by measurement and by calculation. We measured the spectral bandwidth of the monochromator from the Beckman Enzyme Analyzer TR, and found it to be 3.5-4.0 nm (av 3.8) by two different methods. We visually estimated it to be 4 nm. Using the specifications for the diffraction grating, focal length, and fixed slit width, we calculated the theoretical spectral bandwidth to be 3.6 nm.

1. The formulas allow one to determine the optimal slit width and scan amplitude for a given system, which can provide sensitivities higher by 5.4–22.4% than those derived from the previously accepted optimal relation between these parameters as derived without allowance for diffraction. 2. The calculated points have only a small spread around the approximating straight lines, so (10) and (11) can be used for wide ranges in image width. 3. The zero-point sensitivity of such a device has a very broad peak, so the actual parameters do not have to correspond closely to the optimal ones.

Electrical control of slit width by means of the unit described permits continuous adjustment as the wave‐length is changed so that constant energy output of the monochromator may be achieved. As a result, percent absorption is measured directly and the slits are always set for optimum resolving power. An additional feature is curvable slits which are preset for any wave‐length desired. The unit is supplied from an amplifier for automatic output control.

A review is made of published accounts of double-beam attachments for spectrophotometers, for use in the visible and ultra-violet region. A simple alternate-path unit, incorporating a single type 1.P.28 photomultiplier detector, is described. A ratio-recording amplifying system is employed, and the spectrometer slit width is monitored by a servomechanism to give a constant reference output from the amplifier. A compact wavelength drive is incorporated.

A scanning multiple slit assembly (SMSA) has been constructed for the purpose of reducing scatter in medical radiography. The SMSA consists of a series of long, narrow beam-defining slits above the patient that are aligned and synchronously moved with scatter-eliminating slots beneath the patient during an exposure. Evidence, based on measurements of the ratio of scattered-to-primary radiation imaged and radiographs of patients, is presented indicating that such a device is a practical and efficient method of reducing scatter and improving contrast compared to conventional grids. The design considerations and trade-offs associated with the choice of slit width, slit separation distance, and aft slot depth are discussed along with the effect of these parameters on the SMSA's performance. The various problems encountered in obtaining a uniform scan and the manner in which they were handled are also discussed.

A simple expression for designing the slit width of a Czerny-Turner monochromator is derived by optimizing different parameters of the system. A practical application of this formula is illustrated.