Part Of Beam Research Articles

Effective beam separation schemes for the measurement of the electric Aharonov–Bohm effect in an ion interferometer

We propose an experiment for the first proof of the type I electric Aharonov–Bohm effect in an ion interferometer for hydrogen. The performances of three different beam separation schemes are simulated and compared. The coherent ion beam is generated by a single atom tip (SAT) source and separated by either two biprisms with a quadrupole lens, two biprisms with an einzel-lens or three biprisms. The beam path separation is necessary to introduce two metal tubes that can be pulsed with different electric potentials. The high time resolution of a delay line detector allows to work with a continuous ion beam and circumvents the pulsed beam operation as originally suggested by Aharonov and Bohm. We demonstrate that the higher mass and therefore lower velocity of ions compared to electrons combined with the high expected SAT ion emission puts the direct proof of this quantum effect for the first time into reach of current technical possibilities. Thereby a high detection rate of coherent ions is crucial to avoid long integration times that allow the influence of dephasing noise from the environment. We can determine the period of the expected matter wave interference pattern and the signal on the detector by determining the superposition angle of the coherent partial beams. Our simulations were tested with an electron interferometer setup and agree with the experimental results. We determine the separation scheme with three biprisms to be most efficient and predict a total signal acquisition time of only 80s to measure a phase shift from 0 to 2π due to the electric Aharonov–Bohm effect.

Analysis of higher order composite beams by exact and finite element methods

In this paper, a two-layer partial interaction composite beams model considering the higher order shear deformation of sub-elements is built. Then, the governing differential equations and boundary conditions for static analysis of linear elastic higher order composite beams are formulated by means of principle of minimum potential energy. Subsequently, analytical solutions for cantilever composite beams subjected to uniform load are presented by Laplace transform technique. As a comparison, FEM for this problem is also developed, and the results of the proposed FE program are in good agreement with the analytical ones which demonstrates the reliability of the presented exact and finite element methods. Finally, parametric studies are performed to investigate the influences of parameters including rigidity of shear connectors, ratio of shear modulus and slenderness ratio, on deflections of cantilever composite beams, internal forces and stresses. It is revealed that the interfacial slip has a major effect on the deflection, the distribution of internal forces and the stresses.

Negative and positive Goos-Hänchen shifts of partially coherent light fields

The negative and positive Goos-H\"anchen (GH) shifts in reflected light are revisited for a partial coherent light incident on a cavity. A three-level dilute gaseous atomic medium, which follows two-photon Raman transitions, is considered in a cavity. The anomalous (negative group index) and normal (positive group index) dispersions of the intracavity medium lead to negative and positive GH shifts, respectively. The effects of beam width, spatial coherence, and mode index of partial coherent light fields are studied on the negative and positive GH shifts. It is observed that the amplitude of negative and positive GH shifts are relatively large for a small range of beam width and for a small value of spatial coherence of partial coherent light beams. The amplitude of GH shifts becomes small for large beam width and spatial coherence of incident light. Further, the distortion in the reflected light field increases when the amplitude of the GH shifts increases and vice versa.

Partial factors for the design resistance of composite beams in bending

This paper presents the results from a reliability analysis of the resistance of composite beams in sagging bending designed according to Eurocode 4. Using the EN 1990 methodology, the partial factors γM for the structural steel, concrete and shear connection were evaluated. The present study extends earlier work by considering geometrical tolerances given within the published European product and execution standards, which were unavailable during the original calibration of Eurocode 4. Furthermore, recently reported European production data on the yield strength of structural steel is also included. The analyses consider test data from 164 beams with full shear connection, partial shear connection, ductile connectors, non-ductile connectors and beams with high strength steel, which ar?e supplemented with over 3 million simulations. It was found in the present work that the current recommended values for γM were only justified for beams with full shear connection. For beams with partial shear connection, the calculated values of γM were larger than recommended because the partial factor associated with the uncertainty of the resistance model varied considerably. To remedy this situation, conversion factors that are a function of the overall composite beam depth are proposed which, when applied to the design models, justifies lower partial factors than that currently recommended by Eurocode 4.

Analysis Model of Slip for Composite Box Girders

The interface slip of steel–concrete composite beams was studied analytically and numerically. Based on the partial interaction theory, a theoretical solution for the theory of steel–concrete composite box beams with partial shear interaction was derived and equilibrium of the rotation angle w’ was introduced to account for the convenient computation of composite box beam deformation. Numerical simulations of steel–concrete composite box beams subjected to concentrated loads and uniformly distributed loads were conducted. The analytical solutions show an excellent agreement with the numerical results. For typical composite box beams used in practice, shear slip in partial composite box beams makes a significant contribution to beam deformation. Even for full composite box beams, slip effects may result in stiffness reduction. However, many design specifications that use transformed section methods ignore slip effects, except for the American Institute of Steel Construction (AISC) specifications, which recommend a calculation procedure in the commentary. Finally, the proposed method was extended to analyse the interface slip of shear connectors of different pitch and to some extent validate the accurate prediction.

Dynamic analysis of two-layer composite beams with partial interaction using a higher order beam theory

Kant׳s higher order beam kinematics, which takes into account both the longitudinal and transverse higher order deformation of beam, is applied to the dynamic model of two-layer partial interaction composite beams. To establish and solve the mathematical problem, the finite element for the composites is then formulated using the principle of virtual work. Furthermore, the finite element of Timoshenko composite beam model, for the purpose of comparison, is also given in this paper. The numerical performance and reliability of the proposed finite elements are verified through the comparison with the results of ABAQUS using the plane stress model and those based on Reddy׳s higher beam theory and classical beam theories from the literature. Besides, the responses to the seismic and moving load of the proposed composite beam model are also presented, and subsequently the influences of parameters including damping ratio, velocity of moving load, slenderness ratio and interfacial stiffness on the mechanical behavior are studied. Numerical results show that the present higher order composite beam model can achieve higher accuracy on the dynamic analyses than the classical and Reddy׳s models, and the impact effects of moving load together with the partial interaction between sub-layers should be considered.

Photon-monitoring attack on continuous-variable quantum key distribution with source in middle

Motivated by a fact that the non-Gaussian operation may increase entanglement of an entangled system, we suggest a photon-monitoring attack strategy in the entanglement-based (EB) continuous-variable quantum key distribution (CVQKD) using the photon subtraction operations, where the entangled source originates from the center instead of one of the legal participants. It shows that an eavesdropper, Eve, can steal large information from participants after intercepting the partial beams with the photon-monitoring attach strategy. The structure of the proposed CVQKD protocol is useful in simply analyzing how quantum loss in imperfect channels can decrease the performance of the CVQKD protocol. The proposed attack strategy can be implemented under current technology, where a newly developed and versatile no-Gaussian operation can be well employed with the entangled source in middle in order to access to mass information in the EB CVQKD protocol, as well as in the prepare-and-measure (PM) CVQKD protocol.

Interferometry with relativistic electrons

We propose an experiment to test the influence of Lorentz contraction on the interference pattern of a beam of electrons. The electron beam is split and recombined by two pairs of bichromatic laser pulses, using a variation of the Kapitza-Dirac effect. Between the pairs, the electrons are accelerated to relativistic speed. We show that Lorentz contraction of the distance between two partial beams will then lead to a reduction of fringe visibility. The connection of the proposal to Bell's spaceship paradox is discussed.

LINEAR ANALYSIS AND SIMULATION OF INTERFACIAL SLIP BEHAVIOUR FOR COMPOSITE BOX GIRDERS

Abstract The slip at the steel-concrete interface in steel-concrete composite beams was studied analytically and numerically. A theoretical description for steel-concrete composite box beams with partial shear interaction based on the partial interaction theory was derived, and equilibrium of the rotation angle w′ was introduced to allow convenient computation of deformation of composite box beams. Numerical simulations of steel-concrete composite box beams subjected to concentrated load and/or uniformly distributed load were conducted. The analytical solutions show excellent agreement with the numerical results. For typical composite box beams used in practice, shear slip in partial composite box beams makes a significant contribution to beam deformation. Even for full composite box beams, slip effects may result in stiffness reduction. However, slip effects are ignored in many design specifications which use transformed section methods; an exception is the American Institute of Steel Construction [1] specifications, which recommend a calculation procedure in the commentary. Finally, the proposed method was extended to analyze the interface slip for shear connectors of different pitch and, to some extent, confirm the accuracy of the predictions.

Tunable holographic interferometer with a beam-splitting unit and fixed mirrors

This paper presents a holographic interferometer configuration with inclined fixed mirrors based on a beam-splitting unit in which the convergence angle of the partial beams is tuned only by rotating the interferometer relative to the radiation source. The continuous range of tuning is close to the maximum possible (0–180°). The path lengths of the interfering beams are automatically aligned due to the mirror symmetry of the system. The position of the axis of rotation providing minimal aperture limitations in almost the entire range of tuning is determined. A comparison is made with an alternative configuration based on a beam-splitter cube.

Reconfigurable holographic interferometer with fixed mirrors

The configuration of a two-beam interferometer with fixed inclined mirrors for recording holographic gratings is described. The convergence angle of the partial beams is adjusted in the range from 0 to 180° by changing the angle of incidence of the primary beam on the entry edge of the beam-splitting cube without additional adjustment of the mirrors. The path lengths of the interfering beams are automatically aligned by the mirror symmetry of the system. The optimal kinematics of adjusting the convergence angle is found that allows working with beams of sufficiently large diameter in the whole range of adjustment. The interferometer is highly resistive to vibration due to lack of adjustment devices.

Transmission Shift in Fluorescence Microscopy: Adjustable Interference Filters, Theoretical Considerations and Practical Implications

In interference filters, transmitted light bands can be continuously shifted to shorter wavelengths and the filter’s full width of half maximum (FWHM) (synonym: half intensity width/HIW) can be reduced when turned into oblique positions so that the incident axial light no longer runs perpendicularly to the filter’s surface. These modifications of the transmitted light can be described by mathematic functions or particular reference lines empirically evaluated for any filter used. Moreover, potential low intensity leaking rays beyond the filter’s principal transmission band can be shifted or eliminated. The optical effects described can be intensified still more when two interference filters are used as doublet. When the angle of incident light deviates from 90 � , the transmitted light is divided into two partial beams being linearly polarized; their planes of oscillation differ by 90 � , their transmission peaks by 3–7%. Thus, the transmitted light can be modulated further with a rotatable polarizer. In fluorescence microscopy, adjustable interference filters can be used for excitation and suppression in the manner described so that all transmitted light spectra can be modulated in tiny steps and optimally adjusted with regard to the properties of the fluorescent specimen. Several astronomy filters were used for practical evaluations of our method. Because of their particular optical design, these filters could be used for excitation with low-intensity halogen light so that any photobleeching (fading) or other irritations of native specimens could be avoided. Photomicrographs could be taken from living motile fluorescent specimens with a flash-free from indistinctness caused by movement. Our method could be successfully carried out with standard laboratory microscopes based on transmitted light as well as with standard industry microscopes fitted with a vertical illuminator for examinations in incident light, and all images could be significantly improved by transmission shift.

Temporal and spatial coherence properties of free-electron-laser pulses in the extreme ultraviolet regime

The average temporal (longitudinal) and spatial (transverse) coherence of free-electron-laser pulses in the extreme ultraviolet at FLASH is measured by interfering two time-delayed partial beams directly on a CCD camera. Wavelengths between $\ensuremath{\lambda}=32\text{ }\text{ }\mathrm{nm}$ and $\ensuremath{\lambda}=8\text{ }\text{ }\mathrm{nm}$ are examined. A decrease of the coherence time for the fundamental wavelengths from ${\ensuremath{\tau}}_{c}=(6\ifmmode\pm\else\textpm\fi{}0.5)\text{ }\text{ }\mathrm{fs}$ at 32 nm to ${\ensuremath{\tau}}_{c}=(2.9\ifmmode\pm\else\textpm\fi{}0.5)\text{ }\text{ }\mathrm{fs}$ at 8 nm is measured. At $\ensuremath{\lambda}=8\text{ }\text{ }\mathrm{nm}$ the fundamental wavelength and the third harmonic of 24 nm are compared to each other. For 8 nm radiation as third harmonic of 24 nm a coherence time of ${\ensuremath{\tau}}_{c}=(2.5\ifmmode\pm\else\textpm\fi{}0.5)\text{ }\text{ }\mathrm{fs}$ is observed. The spatial coherence of 24 and 8 nm fundamental pulses are found to be very similar. The visibility decreases to 50% of the maximum visibility at about 3.2 mm overlap of the partial beams, which corresponds to 42% of the beam diameter at a distance of 90 m from the exit of the undulator. These results are analyzed in terms of the Gaussian Schell model resulting in six contributing modes to the total radiation. In addition, the correlation of the visibility between the fundamental radiation at 24 nm and its third harmonic at $\ensuremath{\lambda}=8\text{ }\text{ }\mathrm{nm}$ is investigated for identical shots.

Behavior of T-shaped reinforced concrete beams partially confined by structural steel

External confinement of reinforced concrete (R/C) members with structural steel sections or fiber reinforcing wraps is commonly used to improve the flexural behavior of structural members. Flexural strengthening of R/C beams by external steel members is among the most effective and convenient techniques. A study is presented in this paper investigating the flexural behavior of R/C beams having T cross-sections partially confined (P/C) by a combination of various steel members connected together by intermittent batten plates. Four R/C specimens, representing dropped beams in solid slabs, were tested. One control beam had no confinement whereas the three other beams had four steel angles simply wrapped and tied around the stem by batten plates, two angles at the bottom corners of the stem and the other two angles at the stem-flange junctions. Two plates were placed on the top surface of the flange and connected by studs to the two angles at the bottom of the flange. The resulting P/C beams are categorized as partial composite beams because no shear connectors were used between the R/C beam and the jacketing bottom-tension steel angles as in the case of conventional composite beams. All specimens were tested in positive bending under two points loading. Test results revealed an enhancement in the flexural behavior, particularly in the post-yield range of loading, and ductility due to the proposed strengthening and partial composite effect. The number and spacing of the intermittent battens played a significant role in the behavior of the strengthened specimens. Analytical values of loads and deformations at yield and ultimate loading showed good agreement with the measured values.

Application of partial cross-section precast system to save the Amazon forest

The Brazilian civil construction industry is one of the largest consumers of wood in the country. The majority of wood is used as formwork to build concrete structures and is discarded at the end of the construction process. This study presents an innovative structural system that uses a type of partial cross-section precast system with thin reinforced concrete flat plates, which are transported and assembled at the construction site and act as permanent formwork with structural function. The major advantages of this system include the reduction of transport costs; easier assembly of the structural elements because of its low weight; and the possibility of idealizing and designing rigid connections between structural elements, improvement of the structural behavior and postive impact on the material economy. This paper presents construction details, tests results, and some real cases where partial cross-section beams and columns were successfully applied in Brazil.

Delta-sigma subarray beamforming for ultrasound imaging

In this study, an ultrasonic digital beamformer based on subarray processing of 1-bit delta-sigma (\Delta \Sigma ) oversampled echo signals is presented. The single-bit oversampling \Delta \Sigma conversion simplifies the coherent processing in beamforming with improved timing accuracy. Subarray processing also aims to simplify the beamforming complexity, where the partial-beam sums (low-resolution beams) are acquired from small subarrays, and then these partial beams are coherently processed for producing high-resolution beams. In the \Delta \Sigma subarray beamforming, the \Delta \Sigma coded echo signals are summed over the subarray channels, and then these partial beam-sums are first \Delta \Sigma demodulated, then processed for beam-interpolation, followed by coherent summation. This method requires decimation filtering of partial-beam sums from each subarray. The hardware complexity of the \Delta \Sigma subarray beamformer is compared with other beamformers and significant front-end savings are explained. The system is tested experimentally and the results are compared with others using B-scan images reconstructed from archival experimental raw RF data. Both wire targets and cyst phantom are used to show the differences in Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) measurements.

Transmittance of partially coherent flat topped beam with circular and elliptical symmetry in turbulence

Average relative power transmittance is evaluated, for partially coherent flat topped beams with circular and elliptical symmetry, propagated through turbulent atmosphere. We have shown that for partially coherent flat topped beams with the mentioned symmetry, power transmittance is enhanced as the order of flat topped beam increase, but the full coherent one does not show this behavior. Also we have shown that there is a transition region ( R C ) for full and partial coherent flat topped beams with circular and elliptical symmetry. We investigated the dependency of the power transmittance in turbulent media with respect to the structure constant.

On lateral–torsional vibrations of elastic composite beams with interlayer slip

The lateral–torsional vibrations of composite beams are investigated in this paper, based on a variational approach. Composite beams studied in this paper are classified as composite beams with interlayer slip (composite beams with partial interaction or layered wood beams) or three-layer sandwich beams. It will be shown in this paper that both structural systems are governed by the same nature of differential equations. The theoretical framework of lateral–torsional vibrations of composite beams is given, and some engineering results are presented for the pinned–pinned strip composite beam. A simple closed-form solution is achieved for the lateral–torsional natural frequencies. The results are analogous to the ones obtained for the in-plane vibrations of composite beams (sandwich beam or composite beams with partial interaction) where the natural frequencies increase with the stiffness of the connection. Extension of these results to some more complex loading cases is envisaged, and a numerical procedure will be probably needed in the general case.

DYNAMIC CHARACTERISTICS OF PARTIAL COMPOSITE BEAMS

This paper is concerned with the dynamic characteristics of composite beams with partial shear connections. The governing equations of motion for partial composite beams are derived from the one-dimensional partial composite beam theory. By solving the corresponding characteristic equation, the natural frequencies and modal shapes for simple partial composite beams are obtained. The orthogonality condition between the natural modes is utilized to decouple the equations of motion. Closed-form solution for the simple partial composite beam subjected to a moving load is derived by the modal superposition method. Key parameters that govern the fundamental frequency and deflection impact factor of simple partial composite beams are identified. Numerical results show that the former is controlled by the composite connection and section combination parameters, and the latter by the fundamental frequency ratio. It was observed that the time-history response of a partial composite beam may differ significantly from that of a full composite beam in terms of amplitude, period, and overall shape, depending on the composition connection.

Spatio-temporal coherence of free electron laser pulses in the soft x-ray regime

The temporal coherence properties of soft x-ray free electron laser pulses at FLASH are measured at 23.9 nm by interfering two time-delayed partial beams directly on a CCD camera. The partial beams are obtained by wave front beam splitting in an autocorrelator operating at photon energies from h nu = 30 to 200 eV. At zero delay a visibility of (0.63+/- 0.04) is measured. The delay of one partial beam reveals a coherence time of 6 fs at 23.9 nm. The visibility further displays a non-monotonic decay, which can be rationalized by the presence of multiple pulse structure.