摘要:

The noncontact magnetic manipulation of probe masses within the body is an area of research that has received substantial attention from the medical physics community, especially during the past three decades. The therapeutic and diagnostic possibilities arising from such technology include site‐specific drug delivery within the central nervous system, advancement of techniques for navigation and selective catheterization of vessels within the cardiovascular and cerebrovascular systems, and the nonsurgical exploration of the alimentary and respiratory tracts. In this review, we examine the physical principles underlyinginvivomagnetic manipulation systems, and catalog the various types of instrumentation used for such purposes to date. Thereafter, we evaluate the different methods of image‐based localization used to identify the position of the probe within the body. Finally, we appraise an emerging technology known as nonlinear magnetic stereotaxis, a technique that permits minimally invasive access to difficult‐to‐approach parts of the brain. We close the review with a few comments on the directions for future work within this field.

ISSN:0034-6748    

DOI:10.1063/1.1145242

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A novel discharge circuit that reduces significantly the amount of energy conducted by the switch in a TEA CO2laser is reported. We demonstrate this circuit on a working multijoule TEA CO2laser in which the switch is shown to conduct typically only 5% of the total input pulse energy. The laser has worked reliably in gas mixtures that place stringent demands on the discharge and circuit. It has produced an output of 7 J at an efficiency of 9.6% using a CO2:N2:He (1:1:4) gas mixture at atmospheric pressure and further using a helium‐free gas mixture (CO2:N2:H2at 400 mbar) it has produced a maximum efficiency of 14.6% for an output of 7.8 J. The great simplicity and high efficiency of the new discharge circuit allow it to be incorporated in the existing laser designs with minimal modifications.

ISSN:0034-6748    

DOI:10.1063/1.1145118

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Fabry–Perot interferometers are routinely used in the Tore Supra tokamak in order to measure the time evolution of the electron temperature of the confined plasmas. Calibration of such interferometers requires the detection of very low dc levels (0.1 nV) with signal‐to‐noise ratios less than 10−5, which is generally not compatible with standard detection methods. A new correlation method is proposed to achieve this absolute calibration. It is based on a proper noise autocorrelation technique combined with an optimized filtering involving Fourier analysis. The advantages of the method are detailed and experimentally compared to standard averaging techniques, such as coherent addition and synchronous detection. The method can be used in a more general context every time very small amplitude signals are to be measured.

ISSN:0034-6748    

DOI:10.1063/1.1145119

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A simple step‐by‐step procedure, including several novel techniques discussed in the Appendices, is given for minimizing ac phase noise in typical interferometric systems such as two‐beam interferometers, holographic setups, four‐wave mixers, etc. Special attention is given to index of refraction fluctuations, direct mechanical coupling, and acoustic coupling, whose importance in determining ac phase noise in interferometric systems has not been adequately treated. The minimization procedure must be carried out while continuously monitoring the phase noise which can be done very simply by using a photodiode measurement of the interferometer output. Supplementary measurements using a microphone and accelerometer will also be helpful in identifying the sources of phase noise. Emphasis is placed on new techniques or new modifications of older techniques which will not usually be familiar to most workers in optics. Thus, the necessity of eliminating the effects of index of refraction fluctuations which degrade the performance of all interferometers is pointed out as the first priority. A substantial decrease of the effects of all vibrating, rotating, or flowing masses (e.g., cooling lines) in direct contact with the optical table will also have to be carefully carried out regardless of the type of interferometric system employed.It is recommended that this be followed by a simple, inexpensive change to a novel type of interferometer discussed in Appendix A which is inherently less sensitive to mechanical vibration. Such a change will lead to a reduction of both low‐frequency and high‐frequency ac phase noise by more than an order of magnitude and can be carried out for all interferometers with the exception of multiple pass optical systems and high‐resolution FFT spectrometers. It is pointed out that most homemade air bladder vibration isolators are used incorrectly and do not provide sufficient reduction in the contribution of floor vibrations to phase noise. Several simple trampoline‐type air bladder vibration isolator systems are described which are comparable in performance to commercial systems. With the exception of very nonrigid or undamped optical tables, the dominant source of ac phase noise at this point will usually be due to acoustic coupling to the optical components and mounts themselves. This means not only that the optical components and mounts must be rigid but that the mechanical coupling between the table and the mounts, as well as the coupling between the mounts and components themselves, be as rigid as possible.An additional damping of optical mounts beyond that generally found in commercial mountings will also have to be carried out to obtain a further reduction of phase noise. A simple damping technique employing an additional mass and an intermediate damping layer is described which will significantly improve the performance of both homemade and commercial optical mounts. Similar damping techniques which are especially suitable for homemade optical tables and breadboards are also considered.

ISSN:0034-6748    

DOI:10.1063/1.1145120

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new differential refractometer, which mainly consists of a laser light source, a position‐sensitive detector, and a temperature‐controlled refractometer cuvette has recently been developed. In comparison with a conventional differential refractometer, it has a different optical design so that the effect of laser beam drift can be greatly reduced. In our design, a very small pinhole is illuminated by the laser light and the illuminated pinhole is imaged to the detector by a lens located in the middle between the detector and the pinhole in a 2f‐2fconfiguration. The cuvette is placed just before the lens. The pinhole, the cuvette, the lens, and the detector are mounted on a small optical rail. The refractometer can be easily incorporated into any laser light‐scattering spectrometer, in which the laser, the thermostat, and the computer are shared. This not only reduces the total cost (at least ten times cheaper than a commercial differential refractometer), but also enables us to measure the specific refractive index increment and the scattered light intensity under the identical experimental conditions, such as wavelength and temperature. This novel refractometer has a wide linear detection range (±0.035 RI units) with a resolution of 10−6RI units, which is sufficient for determining the specific refractive index increment of most polymer solutions.

ISSN:0034-6748    

DOI:10.1063/1.1145121

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The conversion of a thermospray ionization (TSI) feature of a Finnigan‐MAT TSQ‐70 mass spectrometer to electrospray ionization (ESI) and its performance are described. The existing source, pumping capacity, flanges, and temperature controller of the TSQ‐70 TS feature were used with a few modifications. Conversion of the commercial TS option to a simple and economically viable ES option has made the analysis of large biomolecules possible without expensive upgrades. To preserve the simplicity of the conversion, desolvation is effected by a heated‐capillary tube (HCT). The HCT and its housing are inserted inside the TSQ‐70 TS flange like a solid probe. Mass spectrometric results of low and high molecular weight biomolecules, the mass accuracy, sensitivity, and charge states of the observed ions are comparable to published results by other laboratories. Adequate spectral quality was obtained at short scan times, a required characteristic for interfacing ESI with separation methods such as capillary zone electrophoresis.

ISSN:0034-6748    

DOI:10.1063/1.1145122

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A pinhole small‐angle x‐ray scattering (SAXS) instrument was constructed at the SUNY X3A2 beamline, National Synchrotron Light Source, Brookhaven National Laboratory. The three pinholes were mounted in a thick‐walled stainless steel pipe andprealignedby using a portable laser source and a charge‐coupled device (CCD) area detector. After the prealignment, incorporation of the collimator to the synchrotron x‐ray source required only maximization of the incident x‐ray intensity passing through the pinholes, which could be done easily by using a scintillation counter after proper attenuation. The entire synchrotron SAXS instrument setup took only a few hours even without stepping motor control for the pinhole collimator unit. By combining this collimator with a CCD‐based x‐ray area detector which could be assembled by using commercially available components, the SAXS instrument showed good performance for structural scales up to an order of 100 nm. The CCD‐based x‐ray area detector used a computer‐ (or manually) controlled intensified unit with a variable gain setting in order to accommodate the changing x‐ray flux and to protect the detector from over exposure, a necessary feature for operation of an area detector at a synchrotron light source.

ISSN:0034-6748    

DOI:10.1063/1.1145123

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A complete micropositioning unit based on high precision, manually controlledX‐Y‐Ztranslators, related metrology system, and sighting microscope is described. It has been specifically developed for the alignment of collimating pinholes (5–10 &mgr;m diam) on cryogenic x‐ray detectors, 10–50 &mgr;m in size, deposited both on transparent and opaque substrates. The main characteristics of this flexible and convenient system are the capability to handle a complete test fixture ready for further measurements at cryogenic temperature, coupled with the possibility to verify the precision attained. Such microalignment equipment will find application in optical/UV/x‐ray photon counting experiments, whenever a highly collimated illumination is required or in any test involving precision positioning of small experimental units onto microdevices or detectors.

ISSN:0034-6748    

DOI:10.1063/1.1145124

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

New cassettes for 201 mm×252 mm (8‘×10‘) and 201 mm×400 mm (8‘×15.75‘) storage phosphor plates have been developed at the Synchrotron Resource of the Howard Hughes Medical Institute. The purpose for this work was mainly twofold. Firstly, to diminish the number of manual operations when putting the storage phosphor plate into the cassette or when extracting it from the cassette. Secondly, to render such a cassette much lighter than the former metal cassette previously in use. These two goals were achieved by making new cassettes that are operated as one piece instead of two or three independent parts as with the former systems. The cassettes have been extensively tested and found to be very useful.

ISSN:0034-6748    

DOI:10.1063/1.1145125

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A sealed rigid ‘‘purgebox’’ makes it possible to load air‐ and/or moisture‐sensitive solids into the solids probe inlet of a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer. A pelletized sample is transferred (in a sealed canister) from a commercial drybox to a Lucite(R)purgebox. After the box is purged with inert gas, an attached glove manipulator is used to transfer the sample from the canister to the solids probe of the mass spectrometer. Once sealed inside the inlet, the sample is pre‐evacuated and then passed into the high vacuum region of the instrument at ∼10−7Torr. The purgebox is transparent, portable, and readily assembled/disassembled. Laser desorption FT/ICR mass spectra of the air‐ and moisture‐sensitive solids, NbCl5. NbCl2(C5H5)2, and Zr(CH3)2(C5H5)2are obtained without significant oxidation. The residual water vapor concentration inside the purgebox was measured as 100±20 ppm after a 90‐min purge with dry nitrogen gas. High‐resolution laser desorption/ionization mass spectrometry of air‐sensitive solids becomes feasible with the present purgebox interface. With minor modification of the purgebox geometry, the present method could be adapted to any mass spectrometer equipped with a solid sample inlet.

ISSN:0034-6748    

DOI:10.1063/1.1145126

出版商:AIP    

年代:1994

数据来源: AIP