Frequency performances of a miniature optically pumped cesium beam frequency standard

The optically pumped cesium beam clock named Cs IV is operated with a new short Ramsey cavity satisfying strict requirements on the microwave leakage level. The most relevant characteristics of the device are presented. Cs IV is presently driven by standard electronics coming from a HP 5061 B clock that provides a sinusoidal modulation of the interrogation microwave signal and a microwave power stability of about 1% at a temperature of 20+/-1 degrees C. The short- and medium-term frequency stability measurement gives sigma(y)(1 day)=2x10(-14): this value holds up to 3 days. The accuracy evaluation results in an uncertainty of 10(-12), and the repeatability is evaluated to 3x10(-13). It appears that the flicker floor is beginning at 2x10(-14) and is mainly due to both the power fluctuations of the free running microwave interrogating signal and the fluctuations of the external static magnetic field. The accuracy is limited by the lack of knowledge of the end-to-end cavity phase shift.     

A new approach to calculate the field radiated from arbitrarily structured transducer arrays

A efficient time-domain algorithm, based on the spatial pulse response approach, is proposed for the determination of the acoustic fields radiated by means of acoustical sources. The computations are performed by the discrete representation array modelling (DREAM) procedure, specially adapted to study the planar and arbitrarily structured multielement transducer arrays. DREAM, based on the discrete representation computational concept, acts as the generator of the array velocity potential impulse response, and thus, does not require any analytical solutions prior to the computations. The computations are valid for all field regions and may be performed for any excitation form. Apart from the classic case of rigid baffle conditions, the free and soft planar baffle also can be considered. The use of the time-domain solution for causal Green's function for lossy media enables the wideband absorption effects to be modeled. The accuracy of computations depends on temporal and spatial discretization and can be obtained as required. The quantitative rules, which determine the required discretizations to be predicted, are proposed. The computational examples show that DREAM allows the different and various transducers to be modeled. Its possibilities are illustrated by computations for the multielement transducers, including the beam-steered, amplitude-weighted sonar array, the focusing annular transducer, and the diverging and converging cylindrical array.     

Encrypted optical storage with wavelength-key and random phase codes

An encrypted optical memory system that uses a wavelength code as well as input and Fourier-plane random phase codes is proposed. Original data are illuminated by a coherent light source with a specified wavelength and are then encrypted with two random phase codes before being stored holographically in a photorefractive material. Successful decryption requires the use of a readout beam with the same wavelength as that used in the recording, in addition to the correct phase key in the Fourier plane. The wavelength selectivity of the proposed system is evaluated numerically. We show that the number of available wavelength keys depends on the correlation length of the phase key in the Fourier plane. Preliminary experiments of encryption and decryption of optical memory in a LiNbO(3):Fe photorefractive crystal are demonstrated.     

Polarization multiplexing of diffractive elements with metal-stripe grating pixels

Diffractive elements with polarization multiplexing for the visible spectral region are demonstrated. The polarization-multiplexing property of the element is based on the polarization-dependent transmission characteristics of metal-stripe subwavelength period gratings. The proper dimensions of these gratings are estimated by rigorous calculations. The principle of polarization multiplexing by use of metal-stripe subwavelength period gratings is described for a diffractive element that has a binary amplitude transmission per polarization channel and is demonstrated by experimental results.     

Development of a simulator for radiographic image optimization

A software package, incorporating two computational patient phantoms, has been developed for optimizing X-ray radiographic imaging. A tomographic phantom, visible photographic Man tomographic phantom (VIP-Man), constructed from Visible Human anatomical color images is used to simulate the scattered portion of an X-ray system using the Electron Gamma Shower National Research Council (EGSnrc) Monte Carlo code. The primary portion of an X-ray image is simulated using the projection ray-tracing method through the Visible Human CT data set. To produce a realistic image, the software simulates quantum noise, blurring effects, lesions, detector absorption efficiency, and other imaging artifacts. The primary and scattered portions of an X-ray chest image are combined to form a final image for future observer studies and image quality analysis. Absorbed doses in organs and tissues of the segmented VIP-Man phantom were also obtained from the Monte Carlo simulations. This paper presents methods of the simulator and preliminary results.     

Biomechanical evaluation of nursing tasks in a hospital setting

A field study was conducted to investigate spinal kinematics and loading in the nursing profession using objective and subjective measurements of selected nursing tasks observed in a hospital setting. Spinal loading was estimated using trunk motion dynamics measured by the lumbar motion monitor (LMM) and lower back compressive and shear forces were estimated using the three-dimensional (3D) Static Strength Prediction Program. Subjective measures included the rate of perceived physical effort and the perceived risk of low back pain. A multiple logistic regression model, reported in the literature for predicting low back injury based on defined risk groups, was tested. The study results concluded that the major risk factors for low back injury in nurses were the weight of patients handled, trunk moment, and trunk axial rotation. The activities that required long time exposure to awkward postures were perceived by nurses as a high physical effort. This study also concluded that self-reported perceived exertion could be used as a tool to identify nursing activities with a high risk of low-back injury.     

Multiple paths extraction in images using a constrained expanded trellis

Single shortest path extraction algorithms have been used in a number of areas such as network flow and image analysis. In image analysis, shortest path techniques can be used for object boundary detection, crack detection, or stereo disparity estimation. Sometimes one needs to find multiple paths as opposed to a single path in a network or an image where the paths must satisfy certain constraints. In this paper, we propose a new algorithm to extract multiple paths simultaneously within an image using a constrained expanded trellis (CET) for feature extraction and object segmentation. We also give a number of application examples for our multiple paths extraction algorithm.     

Binding of the tautomeric forms of isoniazid-NAD adducts to the active site of the Mycobacterium tuberculosis enoyl-ACP reductase (InhA): a theoretical approach

The front-line antituberculosis drug isoniazid (INH) inhibits InhA, the NADH-dependent fatty acid biosynthesis enoyl ACP-reductase from Mycobacterium tuberculosis, via formation of covalent adducts with NAD (INH-NAD adducts). While ring tautomers were found the main species formed in solution, only the 4S chain INH-NAD tautomer was evidenced in the crystallized InhA:INH-NAD complex. In this study we attempted to explore the modes of interaction and energy binding of the different isomers placed in the active site of InhA with the help of various molecular modelling techniques. Ligand and enzyme models were generated with the help of the Vega ZZ program package. Resulting ligands were then docked into the InhA active site individually using computational automated docking package AUTODOCK 3.0.5. The more relevant docked conformations were then used to compute the interaction energy between the ligands and the InhA cavity. The AM1 Hamiltonian and the QM/MM ONIOM methodologies were used and the results compared. The various tautomers were found docked in almost the same place where INH-NAD was present as predicted by earlier X-ray crystallographic studies. However, some changes of ligand conformation and of the interactions ligand-protein were evidenced. The lower binding energy was observed for the 4S chain adduct that probably represents the effective active form of the INH-NAD adducts, as compared to the 4R epimer. The two 4S,7R and 4R,7S ring tautomers show intermediate and similar binding energies contrasting with their different experimental inhibitory potency on InhA. As a possible explanation based on calculated conformations, we formulated the hypothesis of an initial binding of the two ring tautomers to InhA followed by opening of only the ring hemiamidal 4S,7R tautomer (possibly catalyzed by Tyr158 phenolate basic group) to give the 4S chain INH-NAD tight-binding inhibitor. The predictions of ligand-protein interactions at the molecular level can be of primary importance in elucidating the mechanisms of action of isoniazid and InhA-related resistances, in identifying the effective mycobactericidal entities and, in further step, in the design of a new generation of antitubercular drugs.     

JAWSAT卫星采用的GPS综合姿态确定系统

本文讨论ＪＡＷＳＡＴ卫星上应用的一种兼用ＧＰＳ，光纤陀螺和太阳敏感器的星上姿态确定系统的研制细节。ＪＡＷＳＡＴ卫星是一顶三轴稳定的小卫星，拟于１９９６年发射入轨。该星目前正由美国空军学院和Ｗｅｂｅｒ州立大学的学生和教师设计制造，主要用于满足教学的需要。本文首先综述该卫星的设计和技术验证实验，然后着重介绍兼用ＧＰＳ和ＦＯＧ定姿的综合姿态确定系统。