Target Hit Research Articles

Determination of workplace neutron spectra at a high energy hadron accelerator using active and passive Bonner sphere spectrometers

In the framework of the 2006 experimental benchmark organized at the GSI (Darmstadt, Germany) by the EC CONRAD network, a neutron dosimetry intercomparison was performed in a workplace field around a carbon target hit by 400 MeV/u C 12 ions. The radiation protection group of the INFN-LNF participated to the intercomparison with a Bonner sphere spectrometer equipped with an active LiI ( Eu ) 6 scintillator and a set of passive detectors, namely MCP-6s ( 80 mg cm - 2 ) /MCP-7 TLD pairs from TLD Poland. Both active and passive spectrometers, independently tested and calibrated, were used to determine the field and dosimetric quantities in the measurement point. The FRUIT unfolding code, developed at the INFN-LNF radiation protection group, was used to unfold the raw BSS data. This paper compares the results of the active or passive spectrometers, obtaining a satisfactory agreement in terms of both spectrum shape and value of the integral quantities, as the neutron fluence or the ambient dose equivalent. These results allow qualifying the BSS based on TLD pairs as a reliable passive method to be used around high energy particle accelerators even in low dose rate areas. This is particularly useful in those workplaces where the active instruments could be disturbed by the presence of pulsed fields, large photon fluence or electromagnetic noise.

Adaptive laser beam projection on an extended target: phase- and field-conjugate precompensation

The problem of adaptive laser beam projection onto an extended object (target) having a randomly rough surface in an optically inhomogeneous medium (atmosphere) is analyzed. Outgoing beam precompensation is considered through conjugation of either the target-return wave phase or the complex field. It is shown that in the presence of "frozen" turbulence, both phase-conjugate (PC) and field-conjugate (FC) precompensation can result in a superfocusing effect, which suggests the possibility of achieving a brighter target hit spot in volume turbulence than in vacuum. This superfocusing effect is significantly more distinct for FC precompensation. In the quasi-stationary case (slowly moving turbulence or target), PC and FC beam control lead to enhanced intensity fluctuations at the target surface associated with intermittent formation and disintegration of bright target hit spots that sporadically attach to the extended target surface. This intensity fluctuation level exceeds intensity fluctuations in the absence of beam control and is higher for FC precompensation. In the nonstationary case, both PC and FC lead to an increase of beam width and centroid wander at the extended target surface compared with conventional projection of a collimated or focused beam.

Eye movements during rapid pointing under risk

We recorded saccadic eye movements during visually-guided rapid pointing movements under risk. We intended to determine whether saccadic end points are necessarily tied to the goals of rapid pointing movements or whether, when the visual features of a display and the goals of a pointing movement are different, saccades are driven by low-level features of the visual stimulus. Subjects pointed at a stimulus configuration consisting of a target region and a penalty region. Each target hit yielded a gain of points; each penalty hit incurred a loss of points. Late responses were penalized. The luminance of either target or penalty region was indicated by a disk which differed significantly from the background in luminance, while the other region was indicated by a thin circle. In subsequent experiments, we varied the visual salience of the stimulus configuration and found that manual responses followed near-optimal strategies maximizing expected gain, independent of the salience of the target region. We suggest that the final eye position is partially pre-programmed prior to hand movement initiation. While we found that manipulations of the visual salience of the display determined the end point of the initial saccade we also found that subsequent saccades are driven by the goal of the hand movement.

No Sex Differences in Memory Formation during General Anesthesia

Women respond differently to anesthesia than men, initially recovering more rapidly, but having more postoperative morbidity. Studies on surgical patients report evidence of memory formation during anesthesia. However, sex differences in memory formation have not been explored. Therefore, the authors investigated sex differences in the implicit and explicit memory formation during general anesthesia. With ethics committee approval, 120 consenting adult patients scheduled to undergo surgery during general anesthesia were recruited. Intraoperatively, 16 target words were presented to patients via headphones, and the Bispectral Index was recorded. Postoperatively, memory for presented words was tested using a word stem completion test. The test was divided into inclusion and exclusion parts, to delineate implicit and explicit memory contributions. Target and distracter hit rates were similar in men and women. For the whole study group, there was a significant difference between inclusion target hit rate (0.42) and base hit rate (0.39) (P = 0.01). Buchner's model suggested that this memory formation was attributable to both implicit and explicit memory. A Bispectral Index value greater than 50 was the only significant predictor of inclusion target hit rate. None of the patients were able to consciously recall the words presented during surgery. Patients showed greater memory performance for words presented during general anesthesia than for words not presented. However, sex differences in memory formation were not observed. A relation between hypnotic state and memory during sevoflurane anesthesia was also established, suggesting that memory formation is possible even at hypnotic depths considered to be adequate anesthesia.

Kinematic patterns associated with accuracy of the drop punt kick in Australian Football

Research into the kinematics of movement associated with the accuracy of the drop punt kick in Australian Football has been limited. The aim of this study was to examine pelvic and lower limb kinematics during the performance of a drop punt kick, in order to identify factors associated with accurate kicking performance. Ten professional Australian Football League (AFL) players performed 20 drop punt kicks towards a target situated 15m away, using their preferred leg. A three-dimensional motion analysis system was used to record the kicking motion from heel contact of the support limb through to ball contact. The subjects were divided into an accurate group (> or =50% accuracy; n=5) and an inaccurate group (<50% accuracy; n=5) based on target hit rate. Kinematic profiles for both kicking and support limbs were compared between the two groups. Results showed that the accurate group had significantly greater hip flexion in both limbs and greater knee flexion in the support limb throughout the kicking movement. The accurate group also had significantly greater anterior pelvic tilt at heel contact (accurate 20.8 degrees ; inaccurate 12.7 degrees ). These data show that kinematic differences in lower limb joint angles may be related to kicking accuracy.

A luminosity monitor for the A4 parity violation experiment at MAMI

A water Cherenkov luminosity monitor system with associated electronics has been developed for the A4 parity violation experiment at MAMI. The detector system measures the luminosity of the hydrogen target hit by the MAMI electron beam and monitors the stability of the liquid hydrogen target. Both are required for the precise study of the count rate asymmetries in the scattering of longitudinally polarized electrons on unpolarized protons. Any helicity correlated fluctuation of the target density leads to false asymmetries. The performance of the luminosity monitor, investigated in about 2000 h with electron beam, and the results of its application in the A4 experiment are presented.

The Integrated Use of Pharmacokinetic and Pharmacodynamic Models for the Definition of Breakpoints

For fluoroquinolones AUC/MIC ratios are known to correlate with clinical outcomes for patients suffering from respiratory tract infections (RTI) and complicated skin and skin structure infections (cSSSI). This paper describes the results of a population PK/PD analysis followed by Monte Carlo simulations to estimate clinical outcome and the microbiological breakpoints for a 400 mg once-daily moxifloxacin (MFX) treatment schedule. Based on PK data from 416 subjects, a non-compartmental population PK model was developed first to describe the expected exposure (AUC) distribution in humans. Height and gender were the main population covariates with moderate influence on PK variability. Albumin, bilirubin, and creatinine clearance (as derived from serum creatinine according to Cockroft and Gault) had a mild effect on AUC. Residual unexplained variability of AUC was low (13.1%). To describe the PD function the MIC distribution pattern of more than 3,000 isolates of S. pneumoniae as the representative pathogen for RTI (MIC90, range: 0.125; 0.006-4 mg/l) was built into the population PK/PD model for RTI, while 126 isolates of methicillin-susceptible Staphylococcus aureus strains (MIC90, range: 0.125; 0.03-4 mg/l) were the basis for the PD function in cSSSI. Simulations for 20,000 (RTI) and 4,000 (cSSSI) subjects were performed to evaluate the AUC/MIC characteristics for moxifloxacin for these two diseases. Overall, a target hit rate was THR = 99% for RTI, while it amounted to THR = 97.5% for cSSSI when applying a threshold of AUIC > 30 [h] as the PK/PD surrogate parameter which is predictive for a positive clinical outcome. A target hit rate of THR = 93.6 % (RTI) and 97.3% (cSSSI), respectively, was predicted when assuming that an AUIC of > 125 [h] is indicative of clinical success (as shown for ciprofloxacin and severe RTIs due to gram-negative infections). In clinical trials with patients receiving 400 mg moxifloxacin once daily for the treatment of community-acquired pneumonia (CAP) success rate was approximately 93.5%. From the simulations performed for RTI an analysis of the overall likelihood of therapeutic failure broken down according to MICs suggests that the risk of a negative clinical outcome at a MIC = 1 mg/l is approximately 0.25% (for MIC = 2 mg/l: predicted likelihood approximately 0.5%) assuming that a cutoff of AUIC = 30 [h] is applicable. Likewise, for cSSSI the probability to fail is predicted as 1.6% at a MIC = 2 mg/l (no strains with MICs between 0.5 and 1 mg/l available from the clinical isolates). These findings are in line with the breakpoint definition of the former National Committee for Clinical Laboratory Standards (NCCLS) for MFX (=1 mg/L to differentiate between susceptible and intermediately susceptible microorganisms; = 2 mg/l to separate intermediate from resistant pathogens). The results of the investigation indicate that the noncompartmental PK/PD model for MFX is suitable to predict clinical outcomes in CAP and cSSSI caused by gram-positive aerobe pathogens. They confirmed that a 400 mg once-daily dosing regimen is suitable to treat these diseases successfully. They are in agreement with the microbiological breakpoints determined by independent methods by the Clinical and Laboratory Standards Institute (CLSI) (former NCCLS).

The HARP TPC

The HARP experiment, at the CERN Proton Synchrotron, measures hadron production cross sections of protons of known momenta (1.5 - 15 GeV/c) impinging on different solid and liquid targets. The HARP TPC provides tracking and particle identification. It is a cylindrical 3D imaging chamber which surrounds the experimental target hit by an extracted beam. The first calibration run was completed and preliminary detector performances for X-rays energy resolution, momentum and d E / d x resolution were evaluated. The preliminary results of an analysis of elastic scattering using a H 2 target completes the evaluation of TPC performance.

Eye–Hand Coordination during Learning of a Novel Visuomotor Task

We investigated how gaze behavior and eye-hand coordination change when subjects learned a challenging visuomotor task that required acquisition of a novel mapping between bimanual actions and their visual sensory consequences. By applying isometric forces and torques to a rigid tool held freely between the two hands, subjects learned to control a cursor on a computer screen to hit successively displayed targets as quickly as possible. The learning occurred in stages that could be distinguished by changes in performance (target-hit rate) as well as by gaze behavior and eye-hand coordination. In a first exploratory stage, the hit rate was consistently low, the cursor position varied widely, and gaze typically pursued the cursor. In a second skill acquisition stage, the hit rate improved rapidly, and gaze fixations began to mark predictively desired cursor positions, indicating that subjects started to program spatially congruent eye and hand motor commands. In a third skill refinement stage, performance continued to improve gradually, and gaze shifted directly toward the target. We suggest that during the exploratory stage, the learner attempts to establish basic mapping rules between manual actions and eye-movement commands. In this process, subjects may establish correlations between hand motor commands and their visual sensory consequences, primarily in fovea-anchored, gaze-centered coordinates, and correlations between recent hand motor commands and eye motor commands. The established mapping rules are then implemented and refined in the skill acquisition and refinement stages.

TU-C-T-617-10: The Use of a Miniature Multileaf Collimator in Stereotactic Proton Therapy

Purpose: To evaluate — in terms of dose conformity, neutron dose, activation, and leakage — the use of a Miniature Multileaf Collimator (MMLC) in stereotactic proton therapy, both as an aperture and for segmented intensity modulated proton therapy (IMPT). Method and Materials: Firstly, we compute the neutron production and activation of the MMLC with Geant4. In a simple geometry — a cylindrical target hit by a pencil proton beam — we determine the neutron distribution as function of position and energy, and compare tungsten,brass,nickel, and lead. Given the point‐spread functions, we assess the secondary‐neutron dose to the patient for the different materials and MMLC distance to patient. Secondly, we model the Radionics ConforMAX™ MMLC as integrated in our stereotactic proton beamline, and compare the dose distributions for the MMLC and an equivalent aperture. The results are validated with radiographic film measurements. Finally, we measure the proton leakage, activation, and neutron dose. Results: The neutron production in tungsten, the leaf material in most MLC's, is more than twice that of nickel. For a 10 cm diameter field, with a range of 15 g/cm2 and modulation of 5 g/cm2, and with the MMLC positioned at 30.0 cm from the patient, the maximum neutron dose, i.e. for a closed MLC, is ∼0.04% of the target dose. The MMLC leaf width at iso center is 3.2 mm; the lateral penumbra in air is 0.6 mm. Conclusion: In beam‐lines with a large SAD, such as our stereotactic beam‐line, the use of the MMLC as aperture is feasible. The device can be positioned far away from the patient, which reduces the neutron dose to acceptable levels, while hardly compromising the lateral penumbra. Given a decrease in proton efficiency of a factor of 3, the MMLC could also be used for IMPT.

Impact of 7-TeV∕c large hadron collider proton beam on a copper target

The large hadron collider (LHC) will allow for collision between two 7TeV∕c proton beams, each comprising 2808 bunches with 1.1×1011 protons per bunch, traveling in opposite direction. The bunch length is 0.5ns and two neighboring bunches are separated by 25ns so that the duration of the entire beam is about 89μs. The beam power profile in the transverse direction is a Gaussian with a standard deviation of 0.2mm. The energy stored in each beam is about 350MJ that is sufficient to melt 500kg of copper. In case of a failure in the machine protection systems, the entire beam could impact directly onto an accelerator equipment. A first estimate of the scale of damage resulting from such a failure has been assessed for a solid copper target hit by the beam by carrying out three-dimensional energy deposition calculations and two-dimensional numerical simulations of the hydrodynamic and thermodynamic response of the target. This work has shown that the penetration depth of the LHC protons will be between 10 and 40m in solid copper. These calculations show that material conditions obtained in the target are similar to those planned for beam impact at dedicated accelerators designed to study the physics of high-energy-density states of matter, for example, the Facility for Antiprotons and Ion Research at the Gesellschaft für Schwerionenforschung, Darmstadt [W. F. Henning, Nucl. Instrum Methods Phys. Res. B 214, 211 (2004)].

The Assessment of Explicit Memory and Implicit Memory after General Anesthesia for Cesarean Section Using the Process Dissociation Procedure

Background: It is still unclear whether intraoperative events result entirely from moments of inadequate anesthesia. We used the process dissociation procedure to estimate implicit and explicit memory for words presented during elective cesarean sections. Methods: Sixty patients undergoing elective cesarean sections were studied. We used a word stem completion test for memory testing. Four lists of words was played via headphones during cesarean section. During testing, two lists were used in the inclusion part (one target and one distractor list); the remaining two lists were used in the exclusion part. BIS was recorded on a computer during word presentation. Results: The duration of surgery was 67.1 13.9 min. The mean BIS during word presentation was 73.4 2.5. In the inclusion part, target hit rates (i.e., the probability of responding sucessfully to a word presented during surgery) were statistically significantly higher than distractor hit rates (0.21 vs. 0.12), and in the exclusion part target hit rates were statistically significantly higher than distractor hit rates (0.17 vs. 0.11). During testing, none of the patients was able to recall the correct words presented during surgery when presented with the word stem aurally and visually. Conclusions: We found evidence of implicit memory after general anesthesia for cesarean section using the process dissociation procedure, and found that implicit memory can occur in the absence of conscious recall.

Neuroelectrical signs of selective attention to color in boys with attention-deficit hyperactivity disorder

In order to gain insight into the functional and macroanatomical loci of visual selective processing deficits that may be basic to attention-deficit hyperactivity disorder (ADHD), the present study examined multi-channel event-related potentials (ERPs) recorded from 7- to 11-year-old boys clinically diagnosed as having ADHD ( n=24) and age-matched healthy control boys ( n=24) while they performed a visual (color) selective attention task. The spatio-temporal dynamics of several ERP components related to attention to color were characterized using topographic profile analysis, topographic mapping of the ERP and associated scalp current density distributions, and spatio-temporal source potential modeling. Boys with ADHD showed a lower target hit rate, a higher false-alarm rate, and a lower perceptual sensitivity than controls. Also, whereas color attention induced in the ERPs from controls a characteristic early frontally maximal selection positivity (FSP), ADHD boys displayed little or no FSP. Similarly, ADHD boys manifested P3b amplitude decrements that were partially lateralized (i.e., maximal at left temporal scalp locations) as well as affected by maturation. These results indicate that ADHD boys suffer from deficits at both relatively early (sensory) and late (semantic) levels of visual selective information processing. The data also support the hypothesis that the visual selective processing deficits observed in the ADHD boys originate from deficits in the strength of activation of a neural network comprising prefrontal and occipito-temporal brain regions. This network seems to be actively engaged during attention to color and may contain the major intracerebral generating sources of the associated scalp-recorded ERP components.

Pressure and stress waves in a spallation neutron source mercury target generated by high-power proton pulses

The international ASTE collaboration has performed a first series of measurements on a spallation neutron source target at the Alternating Gradient Synchrotron (AGS) in Brookhaven. The dynamic response of a liquid mercury target hit by high-power proton pulses of about 40 ns duration has been measured by a laser Doppler technique and compared with finite elements calculations using the ABAQUS code. It is shown that the calculation can describe the experimental results for at least the time interval up to 100 μs after the pulse injection. Furthermore, it has been observed that piezoelectric pressure transducers cannot be applied in the high γ-radiation field of a spallation target.

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Different stress factor signals converge at phosphoinositide turnover in Drosophila cells

1. 1. Drosophila Schneider-2 cells were analysed with regard to calcium concentration, inositol 1,4,5-trisphosphate concentration and heat shock protein synthesis under conditions of heat shock and various chemical stresses in the search for a common target hit by the different signals. 2. 2. Temperature elevation, hydrogen peroxide, arsenite, cadmium, and ethanol induced the typical set of major heat shock proteins, but a sustained increase in cytosolic free calcium concentration was observed only under heat shock conditions. 3. 3. Inositol 1,4,5-trisphosphate, however, was elevated in every case, and substances which activate phosphoinositide turnover, as deoxycholate and saponine, were found to be very potent inducers of the stress response.

Defect diffusion and closed-time distributions for ionic channels in cell membranes.

The ionic channels associated with proteins embedded in cell membranes often show a fluctuating behavior between open and closed states. A feature commonly observed is the long-time tail in the distribution f(t) of closed-state durations. A generalization of a defect-diffusion model recently proposed to explain this behavior is solved analytically for a one-dimensional geometry. The analysis involves the solution of a target annihilation problem with a finite annihilation rate for the target hit by a walker. While at short times f(t) may decay exponentially, at long times the solution is dominated either by a power law or a stretched exponential, depending on the initial defect configuration. The predictions of the model are shown to be in agreement with experimental data.

Steady state penetration of thermoviscoplastic targets

Steady state thermomechanical deformations of a target hit by a rigid cylindrical penetrator with an ellipsoidal nose are studied. The material of the target is assumed to be thermally softening but strain and strain-rate hardening. Results computed and presented graphically include the pressure distribution on the nose of the penetrator, dependence of the axial resisting force upon the speed of the penetrator, and the variation of field quantities such as the temperature and strain-rate in the target. Computed results show that the ratio of the major to minor axes of the ellipsoidal nose has a significant effect on the deformations of the target particles in the vicinity of the penetrator nose.

Priming semantic relations in patients with Huntington's Disease

To investigate the hypothesis that Huntington's Disease involves a breakdown in the organization of the lexico-semantic representational system, mildly and moderately demented patients with Huntington's Disease and age-matched normal control subjects were given a brief battery of language tests and a semantic priming free association task. Results of the language tests provided suggestive, but confounded, evidence for a semantic deficit in Huntington's Disease. Less equivocal evidence was yielded by results of the priming task, which showed a decline in the effect of association strength of primed stimulus-target word pairs on target hit rates. This finding was interpreted as a disruption in the system of spreading activation in a lexico-semantic network. This breakdown was contrasted with the more severe language deficits found in dementias which are primarily cortical in origin.

Role of gain programming in the voluntary movement of the human forearm

The dynamic behaviour of a one-link model of the human forearm is studied. The model reference adaptive aspect and the questions of parameter against signal adaptation are analysed by modelling the neural control mechanisms of the muscles. It is demonstrated that, for a precise target hit, a parameter adaptation scheme, corresponding to a central programming of system gains, is necessary. This programming of gains may shed some light on further functional aspects of the central nervous system.