Slow Scanning Speed Research Articles

Effect of different heating methods on deformation of metal plate under upsetting mechanism in laser forming

In a laser forming process, different forming mechanisms have different deformation behaviors. The aim of laser forming is to acquire plane strain under an upsetting mechanism, while a plate undergoes a small bending deformation. In some industrial applications, the bending strain should not occur. To achieve high-precision forming, the deformation behaviors of a metal plate when an upsetting mechanism plays a dominant role are studied in the paper. Several heating methods are proposed to reduce the plane strain difference along the thickness direction and little bending deformation resulting from a small temperature difference between the top and bottom surfaces of the plate. The results show that negligible bending deformation and a uniform plastic plane strain field can be obtained by simultaneously heating the top and bottom surfaces with the same process parameters. A conventional scanning method needs a larger spot diameter and slower scanning speed under the upsetting mechanism, but a smaller spot diameter and quicker scanning speed may be selected using the simultaneous heating method, which can greatly widen the potential scope of process parameters.

Contour based respiratory motion analysis for free breathing CT

We propose a method to quantify superior–inferior (SI) motion of a rigid target using the 3D contour from free-breathing CT (FBCT). The technique utilizes similarity between 2D contours (Jaccard Index) and a population based density function for probability of motion amplitude, and is applicable both when the static target shape is and is not known beforehand. Simulations and phantom measurements showed that motion reconstruction is often feasible, with decreasing accuracy as discrepancy is introduced between assumed and actual static shape. When no static shape is used the analysis is most robust for slow scanning speeds relative to the motion period.

Selective laser melting of aluminium components

Previous work has shown that the processing of aluminium alloys by selective laser melting (SLM) is difficult, with reasonable components only being produced with high laser powers (minimum 150 W) and slow laser scanning speeds. The high laser power is a significant problem as it is higher than that used in many SLM machines. Also, the combination of high power and low speed creates a large melt pool that is difficult to control, leading to balling of the melt and possible damage to the powder distribution system. Even when processing is carried out successfully, the high power and slow scan speed significantly increase build time and the manufacturing costs. This paper considers the changes that can be made to the SLM process so as to reduce the laser power required and increase the laser scanning rates, while still producing components with a high relative density. It also considers why aluminium and its alloys are much more difficult to process than stainless steels and commercially pure titanium. Two MCP Realizer machines were used to process 6061 and AlSi12 alloys, one processing at 50 W and the other 100 W laser power. Even with an optimum combination of process parameters a maximum relative density of only 89.5% was possible (achieved with 100 W). The major confounding factor for processing aluminium and its alloys was found to be oxidation due to the presence of oxygen within the build chamber. This formed thin oxide films on both the solid and molten materials. It was observed that the oxide on the top of the melt pool vaporised under the laser creating a fume of oxide particles, while melt pool stirring, probably due to Marangoni forces, tended to break the oxide at the base of the melt pool allowing fusion to the underlying tracks. However, the oxides at the sides of the melt pool remained intact creating regions of weakness and porosity, as the melt pool failed to wet the surrounding material. Therefore, if 100% dense aluminium components are to be produced by SLM, using low laser powers, methods need to be developed that can either disrupt these oxide films or avoid their formation.

In vivo non-linear optical (NLO) imaging in live rabbit eyes using the Heidelberg Two-Photon Laser Ophthalmoscope

Imaging of non-linear optical (NLO) signals generated from the eye using ultrafast pulsed lasers has been limited to the study of ex vivo tissues because of the use of conventional microscopes with slow scan speeds. The purpose of this study was to evaluate the ability of a novel, high scan rate ophthalmoscope to generate NLO signals using an attached femtosecond laser. NLO signals were generated and imaged in live, anesthetized albino rabbits using a newly designed Heidelberg Two-Photon Laser Ophthalmoscope with attached 25 mW fs laser having a central wavelength of 780 nm, pulsewidth of 75 fs, and a repetition rate of 50 MHz. To assess two-photon excited fluorescent (TPEF) signal generation, cultured rabbit corneal fibroblasts (RCF) were first labeled by Blue-green fluorescent FluoSpheres (1 μm diameter) and then cells were micro-injected into the central cornea. Clumps of RCF cells could be detected by both reflectance and TPEF imaging at 6 h after injection. By 6 days, RCF containing fluorescent microspheres confirmed by TPEF showed a more spread morphology and had migrated from the original injection site. Overall, this study demonstrates the potential of using NLO microscopy to sequentially detect TPEF signals from live, intact corneas. We conclude that further refinement of the Two-photon laser Ophthalmoscope should lead to the development of an important, new clinical instrument capable of detecting NLO signals from patient corneas.

Software controlling algorithms for the system performance optimization of confocal laser scanning microscope

The relative slow scanning speed of a galvanometer commonly used in a confocal laser scanning microscopy system can dramatically limit the system performance in scanning speed and image quality, if the data collection is simply synchronized with the galvanometric scanning. Several algorithms for the optimization of the galvanometric CLSM system performance are discussed in this work, with various hardware controlling techniques for the image distortion correction such as pixel delay and interlace line switching; increasing signal-to-noise ratio with data binning; or enhancing the imaging speed with region of interest imaging. Moreover, the pixel number can be effectively increased with Acquire-On-Fly scan, which can be used for the imaging of a large field-of-view with a high resolution.

CMOS Sensors for Imaging Blood Flow

Laser Doppler flowmetry is useful for monitoring blood flow, but the slow scanning speed can introduce motion artifacts and make detection of rapid changes impossible. Instruments that incorporate CMOS technology may enable real-time imaging of microcirculation.

Intracellular Myosin Motor Protein Motion Using Laser Scanning Confocal Microscopy

We focus on live cell single molecule imaging and tracking with particular focus on measuring single myosin V steps along actin filaments within live cells. The goal of the work is to acquire information that will offer new insights into the mechanism of these motors' processivity. Conventionally, single molecule Myosin studies have been accomplished through total internal reflection fluorescence microscopy (TIRF).1,2 However, TIRF methods have very limited applicability to live cell in vivo studies. As such, we apply confocal laser scanning microcopy (CLSM) to imaging and tracking of Myosin V. CLSM also offers the capability to provide full 3-dimensional tracking of biomolecular motors. Our experiments have confirmed step size results from previous TIRF experiments. In terms of instrumentation, we overcome the nominally slow scanning speed of CLSM by the use of a fiber scanning technique that allows us to scan with image acquisition times of less than 100 ms. We make use of home-made streptavidin-functionalized quantum dots in conjunction with this tracking technique to increase the quantum efficiency and stability of the fluorophores. The QD fabrication and sample preparation techniques will also be presented.1. A. Yildiz, J. N. Forkey, S. A. McKinney, T. Ha, Y. E. Goldman, and P. R. Selvin, “Myosin V walks hand-over-hand: Single fluorophore imaging with 1.5-nm localization,” Science 300 (5628), 2061-2065 (2003).2. T. Sakamoto, A. Yildez, P. R. Selvin, and J. R. Sellers, “Step-size is determined by neck length in myosin V,” Biochemistry 44 (49), 16203-16210 (2005).

Development of Vacuum Ultraviolet Streak Camera System for the Evaluation of Vacuum Ultraviolet Emitting Materials

Details of the design and development of a bright vacuum ultraviolet Seya–Namioka type spectrometer and streak camera system with reflection-type input optics is presented. The Seya–Namioka spectrometer has a 40 mm by 45 mm holographic grating with a groove density of 600 grooves/mm, linear dispersion of 8 nm/mm, and effective F-number of 4.2. To eliminate loss of light by absorption, the streak camera imaging unit uses Al and MgF2 coated imaging optics with at least 80% reflection from 125–850 nm and has an effective F-number of 4. It is equipped with a synchronized scan unit that can be tuned to 82 MHz and a slow scan speed unit that can measure up to 2-MHz single event. Temporal response of the system at the 20-ns scanning range is evaluated to be around 260 ps.

Burn imaging with a whole field laser Doppler perfusion imager based on a CMOS imaging array

Laser Doppler perfusion imaging (LDPI) has been proven to be a useful tool in predicting the burn wound outcome in an early stage. A major disadvantage of scanning beam LDPI devices is their slow scanning speed, leading to patient discomfort and imaging artifacts. We have developed the Twente Optical Perfusion Camera (TOPCam), a whole field laser Doppler perfusion imager based on a CMOS imaging array, which is two orders of magnitude faster than scanning beam LDPI systems. In this paper the first clinical results of the TOPCam in the setting of a burn centre are presented. The paper shows perfusion images of burns of various degrees. While our system encounters problems caused by blisters, tissue necrosis, surface reflection and curvature in a manner similar to scanning beam imagers, it poses a clear advantage in terms of procedure time. Image quality in terms of dynamic range and resolution appears to be sufficient for burn diagnosis. Hence, we made important steps in overcoming the limitations of LDPI in burn diagnosis imposed by the measurement speed.

A theoretical model for respiratory motion artifacts in free-breathing CT scans

Successful radiotherapy treatment depends heavily upon the accuracy of patient geometry captured during treatment simulation using computed tomography (CT) scans. Radiotherapy patients are often scanned under free breathing, and respiratory motion can cause severe artifacts in CT scans, including shortening, elongation or splitting of the shapes and shifting of the midpoint positions of the tumor and organs. This paper presents a theoretical model that explains the source of motion artifacts and the relationship between motion artifacts and the motion parameters of the scanner, treatment couch and tumor/organ. It is shown that an understanding of the relationship between the translational table velocity and the maximum tumor/organ velocity might enable one to mitigate certain types of motion artifacts. We show that splitting artifacts can be eliminated if the scanning speed is above the maximum tumor/organ velocity. Slow scanning speeds are shown to be useful for obtaining accurate internal target volumes (ITVs), and fast scanning speeds are shown to be useful for obtaining accurate tumor/organ shapes. In both cases, an upper bound on the maximum possible error is calculated as a function of the scanning speed. A set of special scanning speeds which allow for an accurate representation of tumor/organ length along the craniocaudal direction is obtained, and a relationship between the maximum displacement of a tumor/organ image's midpoint position and the magnitude of its length distortion is derived.

Visual and Cognitive Deficits Predict Stopping or Restricting Driving: The Salisbury Eye Evaluation Driving Study (SEEDS)

To determine the visual and other factors that predict stopping or restricting driving in older drivers. A group of 1425 licensed drivers aged 67 to 87 years, who were residents of greater Salisbury, participated. At 1 year after enrollment, this group was categorized into those who had stopped driving, drove only within their neighborhood, or continued to drive beyond their neighborhood. At baseline, a battery of structured questionnaires, vision, and cognitive tests were administered. Multivariate analysis determined the factors predictive of stopping or restricting driving 12 months later. Of the 1425 enrolled, 1237 (87%) were followed up at 1 year. Excluding those who were already limiting their driving at baseline (n = 35), 1.5% (18/1202) had stopped and 3.4% (41/1202) had restricted their driving. The women (odds ratio [OR], 4.01; 95% confidence interval [CI], 2.05-8.20) and those who prefer to be driven (OR, 3.91; 95% CI, 1.91-8.00) were more likely to stop or restrict driving. Depressive symptoms increased likelihood of restricting or stopping driving (OR, 1.08; 95% CI, 1.009-1.16 per point Geriatric Depression Scale). Slow visual scanning and psychomotor speed (Trail Making Test, Part A: OR, 1.02; 95% CI, 1.01-1.03), poor visuoconstructional skills (Beery-Buktenica Test of Visual Motor Integration: OR, 1.14; 95% CI, 1.05-1.25), and reduced contrast sensitivity (OR, 1.15; 95% CI, 1.03-1.28) predicted stopping or reducing driving. Visual field loss and visual attention were not associated. The effect of vision on changing driving behavior was partially mediated by cognition, depression, and baseline driving preferences. In this cohort, contrast sensitivity and cognitive function were independently associated with incident cessation or restriction of driving space. These data suggest drivers with functional deficits make difficult decisions to restrict or stop driving.

Surface nitriding of Ti–6Al–4V alloy with a high power CO 2 laser

Surface nitriding of a Ti–6Al–4V alloy by laser melting in a flow of nitrogen gas has been investigated, with the aim of increasing surface hardness and hence improving related properties such as wear and erosion resistance. The effect of the scanning speed, nitrogen dilution, and nitrogen flow rate on microstructure, microhardness, and cracking of the nitrided layers was studied. Optical, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction (XRD) were used to reveal the microstructure and to identify the phases formed. It is shown that smooth, deep, and crack-free nitride layers of a surface hardness ranging between 500 and 800 HV can be obtained by controlling the processing parameters. Cracks are present in the sample processed at slow scanning speed and high laser power. Dilution of the nitrogen gas with argon gas leads to a crack-free nitride layer at the expense of a reduction in surface hardness. Slow scanning speeds lead to the formation of a deep and hard surface layer, and increasing the nitrogen flow rate results in a rough surface with a slight increase in hardness.

Selective Targeting of the Retinal Pigment Epithelium in Rabbit Eyes with a Scanning Laser Beam

Selective targeting of the retinal pigment epithelium (RPE) with repetitive laser pulses that minimize thermal damage to the adjacent photoreceptors is a promising new therapeutic modality for RPE-related retinal diseases. The selectivity of an alternative, more versatile scanning approach was examined in vivo by using a broad range of scanning parameters. Acousto-optic deflectors repeatedly scanned the focus of a continuous wave (cw)-laser across the retina of Dutch belted rabbits, producing microsecond irradiation at each RPE cell. Two irradiation patterns forming separated lines (SEP) or interlaced lines (INT), different dwell times (2.5-75 micros), and repetition numbers (10 and 100 scans with 100-Hz repetition rate) were tested. Thresholds were evaluated by fundus imaging and angiography. Histology was performed for selected parameters. Selective RPE cell damage was obtained with moderate laser power. The angiographic threshold power decreased with pulse duration, number of exposures, and applying the INT pattern. Ophthalmoscopic thresholds, indicating onset of thermal coagulation, were higher than twice the angiographic threshold for most tested parameters. Histology confirmed selective RPE cell damage for SEP irradiation with 7.5 and 15 micros; slower scan speeds or closed lines caused photoreceptor damage. A cw-laser scanner can be set up as a highly compact and versatile device. Selective RPE damage is feasible with dwell times up to 15 micros. Greatest selectivity is achieved with short exposure times and separated scan lines. Interlaced lines and long exposure times facilitate heat conduction into photoreceptors. A scanner is an attractive alternative for pulsed selective targeting, because both selective targeting and thermal photocoagulation can be realized.

‘N‐in‐one’ strategy for metabolite identification using a liquid chromatography/hybrid triple quadrupole linear ion trap instrument using multiple dependent product ion scans triggered with full mass scan

This paper describes a new strategy that utilizes the fast trap mode scan of the hybrid triple quadrupole linear ion trap (QqQ(LIT)) for the identification of drug metabolites. The strategy uses information-dependent acquisition (IDA) where the enhanced mass scan (EMS), the trap mode full scan, was used as the survey scan to trigger multiple dependent enhanced product ion scans (EPI), the trap mode product ion scans. The single data file collected with this approach not only includes full scan data (the survey), but also product ion spectra rich in structural information. By extracting characteristic product ions from the dependent EPI chromatograms, we can provide nearly complete information for in vitro metabolites that otherwise would have to be obtained by multiple precursor ion scan (prec) and constant neutral loss (NL) analysis. This approach effectively overcomes the disadvantages of traditional prec and NL scans, namely the slow quadrupole scan speed, and possible mass shift. Using nefazodone (NEF) as the model compound, we demonstrated the effectiveness of this strategy by identifying 22 phase I metabolites in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) run. In addition to the metabolites reported previously in the literature, seven new metabolites were identified and their chemical structures are proposed. The oxidative dechlorination biotransformation was also discovered which was not reported in previous literature for NEF. The strategy was further evaluated and worked well for the fast discovery setting when a ballistic gradient elution was used, as well as for a simulated in vivo setting when the incubated sample (phase I metabolites) was spiked to control human plasma extract and control human urine.

Low-voltage high-resolution scanning electron microscope imaging of the uncoated and Cr-coated zeolite Beta

Fine surface features of the uncoated, as-synthesized zeolite Beta and the effect of Cr sputter coating on the appearance of these features were examined using high-resolution (lateral resolution ∼ 2.5 nm) field emission scanning electron microscopy (FE-SEM). The uncoated particles exhibited charging effects despite a reduced accelerating voltage (2 kV). Thus, only rapid scanning at “TV rates”, where an average of multiple frames is acquired, produced useful FE-SEM images. Pyramidal irregularities, resulting in the “saw teeth-like” surface features less than ∼20–30 nm in size, were observed on the uncoated particles. These images did not reveal any texture over flat areas of the surface. Deposition of thin Cr films with a nominal thickness of 1–2 nm reduced/eliminated sample charging so that a slow scanning speed could be used. The resulting images showed better topographic contrast than the images of the uncoated particles. The appearance of fine “teeth” was not affected by sputtering with thin 1–2 nm Cr films. However, the development of a grainy surface texture in the form of nodules smaller than ∼5 nm over flat areas of the surface, which appeared to grow in number density and size (to more than ∼5 nm) with the increasing nominal (up to 10 nm) Cr film thickness, could be observed. This is hypothesized to be the result of Cr particle formation. Sputtering used to deposit thin Cr films did not appear to damage crystal surfaces. Thus, thin (1–2 nm) Cr coatings improve image quality with little or no loss in surface texture resolution.

Laser Absorption Scanning Tunneling Microscopy of Carbon Nanotubes

We report single molecule laser absorption by carbon nanotubes stamped under ultrahigh vacuum onto Si(100)2x1:H surfaces. Absorption is detected by scanning tunneling microscopy. Images are obtained with and without modulated laser excitation using lock-in amplification and a rear-illumination geometry to reduce thermal effects. Noise appears at topographic edges and is analyzed by a quantitative model in terms of scan speed, mechanical instabilities, and feedback current fluctuations at the edge of the nanotubes. Noise due to mechanical instabilities is shown to persist even in the limit of slow scan speed.

Confirmation, refinement, and extension of a study in intrafraction motion interplay with sliding jaw motion.

The interplay between a constant scan speed and intrafraction oscillatory motion produces interesting fluence intensity modulations along the axis of motion that are sensitive to the motion function, as originally shown in a classic paper by Yu et al. [Phys. Med. Biol. 43, 91-104 (1998)]. The fluence intensity profiles are explored in this note for an intuitive understanding, then compared with Yu et al., and finally further explored for the effects of low scan speed and random components of both intrafraction and interfraction motion. At slow scan speeds typical of helical tomotherapy, these fluence intensity modulations are only a few percent. With the addition of only a small amount of cycle-to-cycle randomness in frequency and amplitude, the fluence intensity profiles change dramatically. It is further shown that after a typical 30-fraction treatment, the sensitivities displayed in the single fraction fluence intensity profiles greatly diminish.

Indium Tin Oxide Electrodes Modified with Tris(2,2‘-bipyridine-4,4‘-dicarboxylic acid) Iron(II) and the Catalytic Oxidation of Tris(4,4‘-di-tert-butyl-2,2‘-bipyridine) Cobalt(II)

Indium tin oxide (ITO) electrodes modified by attachment of tris(2,2'-bipyridine-4,4'-dicarboxylic acid) iron(II) are examined. The mode of attachment is believed to be via the COOH functions in a manner similar to attachment of similar carboxylate-containing compounds to TiO2 surfaces. On the surface the complex resides as a stable electrochemically active monolayer. These modified electrodes can efficiently catalyze the oxidation of certain cobalt complexes, specifically, tris(4,4'-di-tert-butyl-2,2'-bipyridine) cobalt(II). On the unmodified ITO surfaces this cobalt complex is essentially electrochemically inert. The catalytic process approaches diffusional control at very slow scan speeds. Also, the electro-catalysis is sufficiently efficient that the peak oxidation current for Co2+, under certain conditions, exceeds the i(p) for the surface oxidation of the adsorbed Fe2+ by >x100 and the current for the uncatalyzed oxidation of Co2+ by considerably more than that.

Influence on mass-selective ion ejection of the phase difference between the drive r.f. and the axial modulation potentials

The phase difference between the drive r.f. and the axial modulation potential is known to influence significantly the mass shift, and all commercial ion trap mass spectrometers use a fixed value for this difference. However, although this important parameter is partly responsible for the good precision achievable today in most commercial ion traps, little discussion on the variation of the phase difference between the drive r.f. and the axial modulation potential has appeared in the literature. We present here an examination of the influence of a low-level axial modulation potential superimposed by capacitive coupling between the electrodes. Low-level axial modulation potentials are used for certain analytical scans such as reverse scan or slow scan speeds. Such low-level potentials help to prevent deterioration of mass resolution due to, for example, the dissociation of the ions during their resonant ejection from the ion trap. Reverse and forward scans are used to illustrate the mass shift and change in resolution, caused by a change in the phase difference between the drive r.f. potential applied to the ring electrode and the axial modulation potential applied on an end-cap electrode, in electrospray ionization mass spectra. Copyright © 2005 John Wiley & Sons, Ltd.

Flat panel computed tomography of human ex vivo heart and bone specimens: initial experience

The aim of this technical investigation was the detailed description of a prototype flat panel detector computed tomography system (FPCT) and its initial evaluation in an ex vivo setting. The prototype FPCT scanner consists of a conventional radiographic flat panel detector, mounted on a multi-slice CT scanner gantry. Explanted human ex vivo heart and foot specimens were examined. Images were reformatted with various reconstruction algorithms and were evaluated for high-resolution anatomic information. For comparison purposes, the ex vivo specimens were also scanned with a conventional 16-detector-row CT scanner (Sensation 16, Siemens Medical Solutions, Forchheim, Germany). With the FPCT prototype used, a 1,024x768 resolution matrix can be obtained, resulting in an isotropic voxel size of 0.25x0.25x0.25 mm at the iso-center. Due to the high spatial resolution, very small structures such as trabecular bone or third-degree, distal branches of coronary arteries could be visualized. This first evaluation showed that flat panel detector systems can be used in a cone-beam computed tomography scanner and that very high spatial resolutions can be achieved. However, there are limitations for in vivo use due to constraints in low contrast resolution and slow scan speed.