Tip Of Rod Research Articles

SU-DD-A1-03: Dosimetric Characterization of Model CS-1 131Cs Source by Thermoluminescence Dosimetry in Liquid Water

Purpose: To determine the dosimetric characteristics of a recently introduced 131 Cs brachytherapy source by performing measurements in liquid water employing thermo‐luminescence dosimeters(TLD).Method and Materials: Small capsules containing 14 mg of lithium fluoride were constructed from capillary tubes and were supported in a water phantom by two plastic jigs. The jigs allowed the capsules to be positioned around a source in circular and spiral patterns designed to permit measurement of dose rate constant, anisotropy function, and radial dose function. The radioactive source was mounted on the tip of a thin graphite rod with its long axis either parallel or perpendicular to the plane of the TLD pattern. To assure confidence in the results, thirteen different seeds were employed, and measurements were performed multiple times. The measureddosimetric parameters were based on the AAPM Task Group 43 formalism. Results: The dose rate constant measured in liquid water was 1.08 cGy/U ± 5%, and was based on the air‐kerma strength standard established by the National Institute of Standards and Technology. Measured values for the anisotropy function F(r,θ) and the radial dose function g(r) also were determined. The results were compared with recently published values. Conclusions: It appears that this is the first time a complete set of dosimetric parameters for a brachytherapy seed has been measured in liquid water. This method avoids the uncertainty introduced by the use of water‐equivalent plastic. Key words: Brachytherapy seed, Solid water, TLD, TG‐43.

SU-FF-T-136: Design of a Jig for Thermoluminescence Dosimetry of Brachytherapy Sources in Liquid Water and the Determination of a Correction Factor for Water-Equivalent Plastics

Purpose: To develop a method for measuring the characteristics of brachytherapy sources in water, rather than in water-equivalent plastics, and to use this method to determine the correction factor for water-equivalent plastic. Method and Materials: Small thermoluminescence dosimeter (TLD) capsules were constructed from capillary tubes to hold 14 mg of lithium fluoride powder. Plastic jigs were designed to hold the capsules in circular pattern around a brachytherapy source, or in a spiral pattern radiating away from the source. The radioactive source was mounted on the tip of a thin graphite rod with its long axis either parallel or perpendicular to the TLD pattern. The jigs were placed in a water phantom to enable measurement of all TG-43 parameters. A Solid Water™ phantom was constructed to hold the TLD capsules in exactly the same circular pattern around the source. TLD measurements were made in water and Solid Water™ at 1.00 cm distance from a model 6711 source to determine a correction factor for the Solid Water™. Similar measurements were also made with a model CS-1 source. Results: The measured correction factor for Solid Water™ was 1.05 +− 0.02 at a distance of 1.00 cm from the model 6711 source. This value is in good agreement with a Monte Carlo-based value published previously. Similar measurements with the model CS-1 source produced the same result within experimental uncertainties. Discussion: The preferred medium for therapy dose measurements is liquid water. However, dosimetry measurements reported in the literature are limited to water-equivalent plastics. The correction factor for plastic phantoms is based on Monte Carlo calculations, and must be validated by actual measurements.

Penetration and failure of lead and borosilicate glass against rod impact

This paper presents the experimental design and results for gold rod impact on DEDF (5.19 g/cm 3) and Borofloat (2.2 g/cm 3) glass by visualizing simultaneously failure propagation in the glass with a high-speed camera and rod penetration with flash radiography. At a given impact velocity, the velocity of the failure front is significantly higher during early penetration than during steady-state penetration of the rod. For equal pressures but different stress states, the failure front velocities determined from Taylor tests or planar-impact tests are greater than those observed during steady-state rod penetration. The ratio of average failure front velocity to rod penetration velocity decreases with increasing impact velocity ( v p) in the range of v p=0.4–2.8 km/s. As a consequence, the distance between the rod tip and the failure front is reduced with increasing v p . The Tate term R T increases with impact velocity.

Manganese-enhanced MRI (MEMRI) of cryoinjury to pig heart

To characterize acute cryoinjury using MEMRI, the left ventricular (LV) anterior wall of exposed pig hearts was brought in 2-min contact with the tip of 25-mm aluminum rod cooled in liquid nitrogen. Thereafter (1.5 h) hearts were excised and perfused with blood/Krebs Henseleit buffer (1:1) within the perfusion chamber inside a 7 T magnet. Spin-echo experiments were performed with 2.0 ms SINC3 pulses, a FOV of 16×16 cm2, TE=8 ms and a data matrix a 128×128 points. The signal acquisition was gated to diastole by the LV dP/dt (TR of 800–1000 ms). T1-weighted images (6 short axis 8-mm slices) were taken prior to and every 5 min after 0.2 mM MnCl2 addition (5–45 min). At the end hearts were injected with a deposit flow tracer (IR676 dye), sliced and stained with triphenyltetrazolium chloride. MnCl2 caused faster and more significant increases in the intensity of normal areas relative to the injured ones. Time courses were fit by the monoexponential function I=I0+ΔImax(1−exp(t/t1)) (Table). The images showed a 5–8 mm deep area of hypointense subepicardial injury (less Mn2+). Histological examination revealed lack of staining with IR676 (no perfusion), deposition of red blood cells and thin necrotic border zone. Thus the cryoinjury results in perfusion blockage by entrapped red blood cells and myocyte death. Tabled 1 Area Parameter, n=6 I0, % ΔImax, % ΔImax/t1, %/min Injury 76±10 37±10 3.2±3.6 Norm 106±12 101±26 24±18 p 0.004 0.003 0.025 Open table in a new tab

Cryoinjury to pig heart: Near-infrared spectroscopic (NIRS) imaging study

To characterize acute cryoinjury using NIRS imaging, the left ventricular (LV) anterior wall of exposed pig hearts was brought in 2-min contact with the tip of aluminum rod (25-mm diameter) cooled in liquid nitrogen. Changes in sub-epicardial oxygen saturation (OS) of hemoglobin (Hb)+myoglobin (Mb) and water content were monitored by NIRS and visible/NIR point spectroscopy over 90-min period. Subepicardial tissue perfusion was evaluated at 60 min using first pass kinetics of intravascular optical tracer indocyanine green (ICG).

Exact and approximate formulas for deflections of an elastically fixed rod under transverse loading

An exact solution is obtained for the nonlinear bending problem of a thin rod elastically fixed at one end and loaded by a transverse concentrated load of constant direction at the other end. The solution is written in parametric form and expressed in terms of the Jacobi elliptic functions. Based on the exact solutions, approximate formulas are proposed for the de.ection of the rod tip.

Study on optical emission analysis of AC air–water discharges under He, Ar and N2 environments

In this paper, hybrid air–water discharges were used to develop an optimal condition for providing a high level of water decomposition for hydrogen evolution. Electrical and optical phenomena accompanying the discharges were investigated along with feeding gases, flow rates and point-to-plane electrode gap distance. The experiments were primarily focused on the optical emission of the near UV range, providing a sufficient energy threshold for water dissociation and excitation. The OH(A 2Σ+ → X 2Π, Δν = 0) band optical emission intensity indicated the presence of plasma chemical reactions involving hydrogen formation. Despite the fact that energy input was high, the OH(A–X) optical emission was found to be negligible at the zero gap distance between the tip of the metal rod and water surface. In the gas atmosphere saturated with water vapour the OH(A–X) intensity was relatively high compared with the liquid and transient phases although the optical emission strongly depended on the flow rate and type of feeding gas. The gas phase was found to be more favourable because of less energy consumption in the cases of He and Ar carrier gases, and quenching mechanisms of oxygen in the N2 carrier gas atmosphere, preventing hydrogen from recombining with oxygen. In the gas phase the discharge was at a steady state, in contrast to the other phases, in which bubbles interrupted propagation of the plasma channel. Optical emission intensity of OH(A–X) band increased according to the flow rate or residence time of the He feeding gas. Nevertheless, a reciprocal tendency was acquired for N2 and Ar carrier gases. The peak value of OH(A–X) band optical emission intensity was observed near the water surface; however in the cases of Ar and N2 with a 0.5 SLM flow rate, it was shifted below the water surface. Rotational temperature was estimated to be in the range of 900–3600 K, according to the carrier gas and flow rate, which is sufficient for hydrogen production.

Deforming biological membranes: How the cytoskeleton affects a polymerizing fiber

We give a theoretical treatment of the force exerted by a fluctuating membrane on a polymer rod tip, taking into account the effects of an underlying biological cytoskeleton by way of a simple harmonic dependence on displacement. We also consider theoretically and experimentally the dynamics of a growing fiber tip under the influence of such a fluctuation-induced membrane force, including the effects of an underlying cytoskeletal network. We compare our model with new experimental data for the growth of hemoglobin fibers within red blood cells, revealing a good agreement. We are also able to estimate the force and membrane/cytoskeletal displacement required to stall growth of, or buckle, a growing fiber. We discuss the significance of our results in a biological context, including how the properties of the membrane and cytoskeleton relate to the thermodynamics of rod polymerization.

Synthesis and Characterization of III-V Rod Shape Semiconductor Nanocrystals

InP and InAs quantum rods were synthesized via the reactions of monodispersed indium droplets with phosphide or arsenide ions, respectively. In these reactions indium droplets, which do not act as a catalyst but rather as a reactant, are completely consumed. For the synthesis of InP and InAs quantum rods with a narrow size distribution, a narrow size distribution of indium particles is required because each indium droplet serves as a template to strictly limit the lateral growth of individual InP or InAs nanocrystals. Free-standing InP (130 Å diameter and 870 Å length) and InAs (180 Å diameter and 745 Å length) quantum rods without residual metallic catalyst at the rod tip were synthesized from the diluted transparent solutions of metallic indium. Both kinds of synthesized nanorods are in the strong confinement regime since the Bohr diameters of InP and InAs are 200 and 700 Å, respectively.

Precise localisation of archaeological findings with a new ultrasonic 3D positioning sensor

This paper presents a new ultrasonic sensor for 3D co-ordinate estimation, which has been especially designed to localize and sketch findings after they are extracted by archaeologists. Classical tasks at paleo-archaeological excavations are: measuring position with metric tapes, drawing a sketch of found object, and introducing all information into a database manually; operations that are not efficient and prone to errors. The positioning system we have designed allows simultaneous characterization of several findings (absolute position, shape, size and orientation) using as a tool a wireless 2-m-long rod, whose lower tip has to be placed on the object under study. The system contains two ultrasonic emitters and employs the time-of-flight (TOF) the ultrasonic signal takes to reach several fixed receivers, and a robust trilateration algorithm to determine the position of the rod tip with 10 mm accuracy. Object position and contour information are automatically transferred to a database in a central computer avoiding manual typewriting. Airflow is the main source of positioning error in outdoor environments, so a strategy based on a differential emitter fixed at a known position is used, which permits to cancel out the effects of uniform air motion.

Dependence of lightning rod efficacy on its geometric dimensions—a computer simulation

A numerical simulation is used to investigate the effect of rod dimensions on lightning attachment to the lightning rod. The effect is studied by considering a sequence of discharge processes, from a corona ignited in a slowly rising thundercloud electric field to the development of an upward leader in the electric field of an approaching downward leader. It is concluded that the efficacy of a lightning rod is almost independent of the rod radius in the range 0.05–5 cm. This is in agreement with measurements of the breakdown voltage in long laboratory rod-to-plane air gaps for various rod tip radii but is at variance with the conclusions reached by Moore et al (2000a Geophys. Res. Lett. 27 1487, 2000b J. Appl. Meteorol. 39 593, 2003 J. Appl. Meteorol. 42 984) from their observations under thunderstorm conditions.

Malignant melanoma of the choroid associated with misdiagnosed ocular melanocytosis

A 73-year-old white female complained of a darker left eye since childhood, which was interpreted at ophthalmic review some 40 years ago as ‘benign conjunctival melanosis’. Since then, the subject had not consulted an ophthalmologist until this occasion, when she presented with blurry vision OS. On slit-lamp examination, the whole left episclera was seen to show pronounced perivascular melanocytic pigmentation (1, 2). The left iris and choroid also appeared more darkly pigmented. In the periphery, a melanocytic tumour was detected with penetration of the retina and collateral retinal detachment (Fig. 3). The left eye was enucleated. Histological examination revealed an epitheloid cell type melanoma (3, 4) with vitreous invasion and widespread tumour cell seeding 3-5). A dense accumulation of melanocytes as a typical feature of ocular melanocytosis (OM) was found in the uvea, trabecular meshwork, sclera and episclera, especially perivascularly (2, 6). Left eye with brownish subconjunctival pigmentation. Perivascular distribution of episcleral melanocytes. Inset: Masson-trichrome staining: superficial episcleral melanocytes adjacent to blood vessels. The superiorly located choroidal melanoma has penetrated through the retina with strands of malignant cells in the vitreous (arrow). (A) Ultrasonography shows posterior vitreous detachment (arrow). (B) Periodic acid-Shiff staining: epitheloid cell choroidal melanoma penetrates the Bruch's membrane (arrowhead). (C) Masson-trichrome staining: scleral infiltration (arrowheads). Deposits of melanoma cell cover the inferior retina (arrows). Inset: Masson-trichrome staining: melanophages and melanoma cells overlie the retina (arrowhead). Masson-trichrome staining: a typical accumulation of melanocytes in the iris stroma, ciliary body and trabecular meshwork. As a relatively rare condition (with a prevalence of approximately 0.04% among white populations and 0.014% among black populations), congenital OM is often associated with uveal melanomas (Gonder et al. 1982). The lifetime risk of developing uveal melanoma in white OM populations has been estimated to be about 1 : 400, as opposed to 1 : 13 000 for the general white population (Singh et al. 1998). To avoid misdiagnosis as conjunctival melanocytosis (CM), as described in the present report, OM can easily be differentiated from CM. In contrast to OM, CM can be moved over the sclera with a glass rod or cotton tip applicator after topical anaesthesia. Conjunctival melanocytosis is not associated with iris, scleral or choroidal hyperpigmentation. The CM is brownish, whereas episcleral pigment usually has a greyish to bluish tint in OM (Yanoff & Zimmerman 1967; Rummelt & Naumann 1997). Because of an approximately 32-times increased lifetime risk of developing uveal melanomas, patients with OM need to be educated regarding this risk and should be followed with annual lifelong ophthalmoscopic review. This study was supported in part by the Alexander von Humboldt Foundation, Bonn, Germany and the Royal Australian and New Zealand College of Ophthalmologists (RMC).

Safe and Reliable Sound Threshold Measures with Direct Vibration of the Ossicular Chain

The aim of the study was to evaluate the safety and feasibility of piezoelectric malleus vibration audiometer (MVA), which presents micromechanical vibrations to the umbo membranae tympani. Phase I study performed in a tertiary referral center (University Hospital). The coupling rod of the MVA was moved slowly through the outer ear canal toward the eardrum with a micromanipulator. Coupling was completed when the rod tip touched the umbo membranae tympani. Basic audiologic measures of sound threshold obtained with direct stimulation of the malleus are presented. We used MANOVA (multivariate repeated measures ANOVA) to investigate the repeatability of MVA thresholds from one day to the other and when decoupling and retracting the coupling rod 2 mm off the umbo. We also selected the MANOVA to test for unwanted bone-conduction threshold shifts after MVA application. We assessed normality of the data by quantile-quantile plots of the residuals. Twenty-eight male and 10 female subjects with normal hearing, 22.2 to 34.6 years old (median age, 27.2 yr) underwent an examination. Thirty-six subjects underwent MVA, because 2 of the 38 subjects who volunteered for the study have not undergone the procedure due to the external auditory canal anatomy preventing application of the MVA. The results show that it is possible to safely and reliably measure thresholds of direct vibration of the ossicular chain. Using pure tone audiograms, no pure tone bone- and/or air-conduction threshold shifts occurred after the procedure. None of the subjects reported any other ear-related symptoms such as vertigo, tinnitus, or dizziness. Geometric mean vibratory displacements at threshold ranged from 0.55 nm at 250 Hz to 0.03 nm at 6 kHz. MANOVA demonstrated a repeatability of MVA thresholds. Malleus vibration audiometry will not allow exact linkage of actual implantable hearing aid. But the present study demonstrates that MVA can provide an audiometric tool for assessing ossicular function and integrity prior to implantation of an electronic hearing amplifier.

The force generated by biological membranes on a polymer rod and its response: statics and dynamics.

We propose a theory for the force exerted by a fluctuating membrane on a polymer rod tip. Using statistical mechanical methods, the expression for the generated force is written in terms of the distance of the rod tip from the membrane "frame." We apply the theory in calculating the stall force and membrane displacement required to cease the growth of a growing fiber induced by membrane fluctuations, as well as the membrane force and membrane displacement required for rod/fiber buckling. We also consider the dynamics of a growing fiber tip under the influence of a fluctuation-induced membrane force. We discuss the importance of our results in various biological contexts. Finally, we present a method to simultaneously extract both the rigidity of the semiflexible rod and the force applied by, e.g., the membrane from the measurements of the bending fluctuations of the rod. Such a measurement of the force would give information about the thermodynamics of the rod polymerization that involves the usual Brownian ratchet mechanism.

Magnetically insulated electron flow with ions with application to the rod-pinch diode

A one-dimensional, steady-state, relativistic electron-flow model is developed that describes magnetically insulated electron flow in the presence of ions produced by space-charge-limited emission from the anode. The model is applied to the rod-pinch diode which is a cylindrical pinched-beam diode consisting of a small radius anode rod extending through the hole of an annular cathode. The diode is designed to run at critical current so that electrons emitted from the cathode are magnetically insulated and flow axially along the anode rod until they pinch radially onto the rod tip. Ions are emitted along the length of rod and flow radially outward. Without these ions, magnetically insulated electron flow cannot be established and electrons cannot propagate to the rod tip. Both fluid and Vlasov treatments of the electrons are considered. An analytic expression for the critical current is derived and is compared with the critical current determined from experimental data and particle-in-cell simulations. Reasonable agreement is obtained when the electron flow is nonlaminar, suggesting that a significant radial electron pressure is required to correctly describe the flow.

Ultra-high electron beam power and energy densities using a plasma-filled rod-pinch diode

The plasma-filled rod-pinch diode is a new technique to concentrate an intense electron beam to high power and energy density. Current from a pulsed power generator (typically ∼MV, MA, 100 ns pulse duration) flows through the injected plasma, which short-circuits the diode for 10–70 ns, then the impedance increases and a large fraction of the ∼MeV electron-beam energy is deposited at the tip of a 1 mm diameter, tapered rod anode, producing a small (sub-mm diameter), intense x-ray source. The current and voltage parameters imply 20–150 μm effective anode-cathode gaps at the time of maximum radiation, much smaller gaps than can be used between metal electrodes without premature shorting. Interferometric diagnostics indicate that the current initially sweeps up plasma in a snowplow-like manner, convecting current toward the rod tip. The density distribution is more diffuse at the time of beam formation with a low-density region near the rod surface where gap formation could occur. Particle simulations of the beam formation phase are dominated by rapid field penetration along the anode and radial J×B forces leading to gap formation and high-energy beam propagation to the rod tip. Beam deposition at the rod tip produces a high thermal energy-density (∼0.75 MJ/cm3), highly ionized (Z∼10, T∼25 eV) expanding tungsten plasma. Potential applications of this technique include improved radiography sources, high-energy-density plasma generation, and intense 10–100 keV x-ray production for nuclear-weapon-effects testing.

Geometric, But Not Kinetic, Properties of Tools Affect the Affordances Perceived by Toddlers

We asked what rod properties affected children's reaching range. Children, 2 to 4 years old, held a rod (length 10-60 cm) with the tip in the air, walked toward a toy on a table, chose a place to stop, and displaced the toy with the rod's tip. In 2 experiments rod length, mass, and mass distribution were manipulated to determine whether and how geometric and kinetic properties affected chosen distance and posture. Chosen distance depended only on the length of the rod. Postures were affected by length and mass properties of the rod. Not all adaptations in posture were prospectively reflected in the distance. Although we found variations over age, we did not find clear developmental trends. The results are discussed in broader perspectives of development of affordances and tool use.

A Nodal and Finite Difference Hybrid Method for Pin-by-Pin Heterogeneous Three-Dimensional Light Water Reactor Diffusion Calculations

An innovative hybrid spatial discretization method is proposed to improve the computational efficiency of pin-wise heterogeneous three-dimensional light water reactor (LWR) core neutronics analysis. The newly developed method employs the standard finite difference method in the x and y directions and the well-known nodal methods [nodal expansion method (NEM) and analytic nodal method (ANM) as needed] in the z direction. Four variants of the hybrid method are investigated depending on the axial nodal methodologies: HYBRID A, NEM with the conventional quadratic transverse leakage; HYBRID B, the conventional NEM method except that the transverse-leakage shapes are obtained from a fine-mesh local problem (FMLP) around the control rod tip; HYBRID C, the same as HYBRID B except that ANM with a high-order transverse leakage obtained from the FMLP is used in the vicinity of the control rod tip; and HYBRID D, the same as HYBRID C except that the transverse leakage is determined using the buckling approximation instead of the FMLP around the control rod tip. Benchmark calculations demonstrate that all the hybrid algorithms are consistent and stable and that the HYBRID C method provides the best numerical performance in the case of rodded LWR problems with pin-wise homogenized cross sections.

Electrode material transport and re-deposition in high-intensity arc discharge lamps

A two-dimensional model of sintered electrode activator (in particular, barium) transport in the arc discharge lamp tube volume has been developed, based on a numerical solution of the non-stationary diffusion equation. The dependence of the barium atom flow density at the electrode rod tip on fill gas pressure and electrode dimensions has been calculated. It has been found that the main mechanism of activator transport to the rod tip is evaporation from the sintered body and diffusion through the gas. Evolution of tungsten rod emission characteristics caused by deposition of the evaporated material on its surface has been studied experimentally.

Growth of InP nanostructures via reaction of indium droplets with phosphide ions: synthesis of InP quantum rods and InP-TiO2 composites.

InP quantum rods were synthesized via the reaction of monodispersed colloidal indium droplets with phosphide ions. In(0) droplets, which do not act as a catalyst but rather a reactant, are completely consumed. The excess electrons that are produced in this reaction are most likely transferred to an oxide layer at the indium surface. For the synthesis of InP quantum rods with a narrow size distribution, a narrow size distribution of In(0) particles is also required because each indium droplet serves as a template to strictly limit the lateral growth of individual InP nanocrystals. Free-standing quantum rods, 60, 120, or 150 A in diameter, with aspect ratios of 1.6-3.5, and without the residual metallic catalyst at the rod tip, were synthesized from the diluted transparent solution of metallic indium particles. The same approach was used to synthesize InAs quantum rods. A photoactive InP-TiO(2) composite was also prepared by the same chemical procedure; InP nanocrystals grow as well-defined spherical or slightly elongated shapes on the TiO(2) surface.