Bremsstrahlung radiation detection for small animal imaging using a CCD detector

The use of optical methods for the detection of radionuclides is becoming an established tool for preclinical molecular imaging experiments. In this paper we present a set of proof of principle experiments showing that planar bremsstrahlung radiation images can be detected with an intensifying screen using a small animal optical imager based on charge coupled device detector.We develop a bremsstrahlung source using a ³²P-ATP vial placed in a Plexiglas box, the source with an intensifying screen on top was placed inside a small animal optical imaging system. Bremsstrahlung radiation images were produced with the ³²P-ATP source only and also with a pair of pliers placed between the source and the screen. We found that the pair of pliers absorption image matches the shape of the object.Spatial resolution measurements were not performed however, the bremsstrahlung image of the pliers show that the resolution is relatively poor due to a large penumbra effect.We conclude that it is possible to produce planar bremsstrahlung images using optical imaging devices.     

Experimental study of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort laser pulses with intensities of up to ∼1019 W/cm2

Results from experimental studies of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort laser pulses with intensities of up to ～10¹⁹ W/cm² are presented. The continuous spectra of hard X-ray emission from Ta and Al targets and the line spectrum of copper were measured. The temperature of fast electrons was obtained from the measured hard X-ray spectra, and the K_α radiation yield from Ta was measured. The energy conversion efficiency of laser radiation into the copper characteristic radiation was obtained from the measured yield of K_α radiation.     

Simulations of Flexible Manifolds

Monte Carlo simulations of flexible two-dimensional model membranes embedded in three space dimensions are reported. We explain in detail the techniques how to simulate fluid open membranes and fluid closed membranes (vesicles). It is shown that polymerized open membranes are rough and flat. Accordingly, the two larger components of the inertia tensor are proportional to the number of monomers of the surface, λ₃ ≈ λ₂ ～ N, whereas the smallest λ₁ ～ N ^0.65. Polymerized vesicles are isotropic and their mean square radius of gyration is R ² ～ λ _k ～ N. In contrast, fluid membranes and vesicles exhibit crumpled shapes with λ _k ～ N ^0.8 for k = 1,2,3. A monomer on a fluid surface exhibits a time-dependent mean squared displacement of r ² (t) ～ t ^0.8.     

Light-scattering spectroscopic study of polysaccharide protein conjugate

By combining gel permeation chromatography (GPC) and light-scattering spectroscopy, including photon correlation and angular distribution of absolute scattered intensity, we were able to characterize immunologically active Haemophilus influenzae type b polysaccharide (HIB Ps) bovine serum albumin (BSA) conjugates in terms of equivalent hydrodynamic radius r_h ～ (6.2 ± 0.6) × 10² Å, apparent radius of gyration r_g ～ (5.4 ± 0.3) × 10² Å, apparent molecular weight M_w ～ (3.5 ± 0.4) × 10⁶ g/mol, and a second virial coefficient A₂ ～ (1.9 ± 0.3) × 10^?4 cm³ mol/g². We could study the effects of each of the processes in the conjugate formation according to the following procedure: BSA (dialysis, modification, fractionation) + HIB Ps → HIB Ps/BSA conjugate (conjugate formation, fractionation). Narrow distributions of HIB Ps BSA conjugate formation can be achieved using fractionated BSA.     

9OSr +90Y bremsstrahlung efficiency predicted for humans

Summary Bremsstrahlung x-rays are produced when energetic-particles are emitted and absorbed. Measurements of total-body bremsstrahlung efficiency (x-ray photon output per Ci⁹⁰Sr in the body, relative to that in water) have been made in the intact mouse, rat, rabbit, and dog sacrificed 2 weeks after the injection of⁹⁰Sr +⁸⁵Sr. Efficiencies were determined by a comparison of the bremsstrahlung output from⁹⁰Sr + its daughter⁹⁰Y and the gamma-ray emission of⁸⁵Sr. Results were checked by a-assay of the ashed animals. Bremsstrahlung efficiencies averaged 1.10 in a 0.04 kg mouse, 1.14 in a 0.13 kg rat, 1.23 in a 2.6 kg rabbit, and 1.32 in an 8.5 kg beagle. Extrapolating to a 70 kg human, a relative bremsstrahlung efficiency of about 1.4 is predicted. An estimate was made of the⁹⁰Sr body content in a former dial painter based on in vivo counting and a bremsstrahlung efficiency of 1.39 predicted for a 55 kg human female by these animal data. Our value of 1.42 ± 0.08 Ci⁹⁰Sr was in good agreement with corresponding results reported for this subject by 8 other laboratories.Supported by USERDA Contract E (11-1)-119     

Towards predicting Ca2+‐binding sites with different coordination numbers in proteins with atomic resolution

Ca²⁺‐binding sites in proteins exhibit a wide range of polygonal geometries that directly relate to an equally‐diverse set of biological functions. Although the highly‐conserved EF‐Hand motif has been studied extensively, non‐EF‐Hand sites exhibit much more structural diversity which has inhibited efforts to determine the precise location of Ca²⁺‐binding sites, especially for sites with few coordinating ligands. Previously, we established an algorithm capable of predicting Ca²⁺‐binding sites using graph theory to identify oxygen clusters comprised of four atoms lying on a sphere of specified radius, the center of which was the predicted calcium position. Here we describe a new algorithm, MUG (MUltiple Geometries), which predicts Ca²⁺‐binding sites in proteins with atomic resolution. After first identifying all the possible oxygen clusters by finding maximal cliques, a calcium center (CC) for each cluster, corresponding to the potential Ca²⁺ position, is located to maximally regularize the structure of the (cluster, CC) pair. The structure is then inspected by geometric filters. An unqualified (cluster, CC) pair is further handled by recursively removing oxygen atoms and relocating the CC until its structure is either qualified or contains fewer than four ligand atoms. Ligand coordination is then determined for qualified structures. This algorithm, which predicts both Ca²⁺ positions and ligand groups, has been shown to successfully predict over 90% of the documented Ca²⁺‐binding sites in three datasets of highly‐diversified protein structures with 0.22 to 0.49 Å accuracy. All multiple‐binding sites (i.e. sites with a single ligand atom associated with multiple calcium ions) were predicted, as were half of the low‐coordination sites (i.e. sites with less than four protein ligand atoms) and 14/16 cofactor‐coordinating sites. Additionally, this algorithm has the flexibility to incorporate surface water molecules and protein cofactors to further improve the prediction for low‐coordination and cofactor‐coordinating Ca²⁺‐binding sites. Proteins 2009. © 2008 Wiley‐Liss, Inc.     

Roles of ATP and NADPH in formation of the fe-s cluster of spinach ferredoxin

Ferredoxin (Fd) in higher plants is encoded by a nuclear gene, synthesized in the cytoplasm as a larger precursor, and imported into the chloroplast, where it is proteolytically processed, and assembled with the [2Fe-2S] cluster. The final step in the biosynthetic pathway of Fd can be analyzed by a reconstitution system composed of isolated chloroplasts and [³⁵S]cysteine, in which [³⁵S]sulfide and iron are incorporated into Fd to build up the ³⁵S-labeled Fe-S cluster. Although a lysed chloroplast system shows obligate requirements for ATP and NADPH, in vitro chemical reconstitution of the Fe-S cluster is generally thought to be energy-independent. The present study investigated whether ATP and NADPH in the chloroplast system of spinach (Spinacia oleracea) are involved in the supply of [³⁵S]sulfide or iron, or in Fe-S cluster formation itself. [³⁵S]Sulfide was liberated from [³⁵S] cysteine in an NADPH-dependent manner, whereas ATP was not necessary for this process. This desulfhydration of [³⁵S]cysteine occurred before the formation of the ³⁵S-labeled Fe-S cluster, and the amount of radioactivity in [³⁵S]sulfide was greater than that in ³⁵S-labeled holo-Fd by a factor of more than 20. Addition of nonradioactive sulfide (Na₂S) inhibited competitively formation of the ³⁵S-labeled Fe-S cluster along with the addition of nonradioactive cysteine, indicating that some of the inorganic sulfide released from cysteine is incorporated into the Fe-S cluster of Fd. ATP hydrolysis was not involved in the production of inorganic sulfide or in the supply of iron for assembly into the Fe-S cluster. However, ATP-dependent Fe-S cluster formation was observed even in the presence of sufficient amounts of [³⁵S]sulfide and iron. These results suggest a novel type of ATP-dependent in vivo Fe-S cluster formation that is distinct from in vitro chemical reconstitution. The implications of these results for the possible mechanisms of ATP-dependent Fe-S cluster formation are discussed.     

Feasibility of stabilizing a vacuum-diode X-ray source with a laser-plasma cathode

Results are presented from experimental studies of discharge instabilities and the energy and temporal characteristics of a vacuum-diode X-ray source with a laser plasma cathode over a wide range of energies, intensities, and durations of the plasma-forming laser pulse. It is experimentally shown that the vacuum-discharge dynamics and radiation processes in different discharge stages substantially depend on the parameters of the laser radiation. The shortest recorded pulse duration (10 ns) of Ti K-line radiation (4.5 keV) with a total photon number of 10¹¹ is achieved when the laser plasma cathode is produced by a laser pulse with a duration of 27 ps and an intensity of 10¹³ W/cm². It is found that the contrast of characteristic emission against the bremsstrahlung background is maximum when discharge instabilities are suppressed and the accelerating voltage is three to four times higher than the threshold voltage for line excitation.     

Molecular weight and subunit composition of GABAA-ergic compound-sensitive Cl−, HCO 3 − -Stimulated Mg2+ ATPase from the plasma membrane of carp brain (Cyprinus carpio L.)

Molecular weight and subunit composition of Cl^?, HCO ₃ ^? , and picrotoxin-stimulated Mg²⁺-ATPase solubilized with sodium deoxycholate from the plasma membrane fraction of fish brain were studied by gel filtration. These enzymes were eluted from a Sephacryl S-300 column as a single peak and corresponded to a ～300 kDa protein with a Stokes radius of 5.4 nm. The enzyme-enriched fraction concentrated and denatured by SDS was eluted from a Sephacryl S-200 column as a single subunit with a molecular weight of ～56 kDa. SDS-PAGE also revealed a single major protein band with a molecular weight of ～56 kDa. It was concluded that the molecular weight and subunit composition of Cl^?, HCO ₃ ^? -stimulated Mg²⁺-ATPase isolated from the plasma membrane of fish brain are similar to those of GABA_A/benzodiazepine receptor complex from fish brain but differ from those of P-type transport ATPases.     

Theory of the polarization bremsstrahlung from thermal electrons scattered by the Debye sphere of an ion in a plasma

The polarization bremsstrahlung from thermal electrons scattered by the Debye sphere of an ion in a plasma is studied in the quasiclassical approximation. The model of the local plasma frequency is used to check the validity of the asymptotic expression for the polarizability of the electron cloud of an ion in the high-frequency range. This asymptotic expression is then used to derive a formula for the intensity of the total effective polarization bremsstrahlung. The R factor (the ratio of the contribution from the polarization bremsstrahlung to the contribution from conventional static bremsstrahlung) is obtained as a function of the plasma coupling parameter and electron density in order to analyze the role of the polarization bremsstrahlung in the total bremsstrahlung of the thermal plasma electrons. The spectral intensity of the effective polarization bremsstrahlung is calculated in the rotational approximation, which was previously employed in the theory of conventional static bremsstrahlung. It is shown that the spectral intensity of the polarization bremsstrahlung from thermal electrons scattered by the Debye sphere around an ion, as compared with the polarization bremsstrahlung by fast superthermal electrons, decreases more gradually with increasing frequency.     

X-ray Fluorescence (XRF) Analysis of Soil Heavy Metal Pollution from an Industrial Area in Kumasi,Ghana

Knowledge of soil heavy metal concentration is very important for assessing the purity and quality of the soil in an environment. The concentrations of nine heavy metals (NHM), Zn, Pb, Cr, Cu, Co, Ni, Cd, Hg, and As, from the near-surface soils (～ 0–15 cm) from an industrial cluster in Kumasi, Ghana, were qualitatively and quantitatively measured and analyzed using X-ray fluorescence (XRF) spectroscopy analysis. The sources of these NHM were mainly anthropogenic as a result of the indiscriminate industrial waste disposal. In all, a total of about 100 soil samples were taken from six sampling sites, four of which were industrial and the remaining two residential. Forty soil samples out of the total number were carefully selected for elemental analyses and the mean heavy metal concentrations were calculated using statistical methods. The results from locations of high industrial impact showed that the mean concentrations of the NHM present in the soil were in the order of Zn (189.2?908.6 mgkg^?1), Pb (133.7?571.3 mgkg^?1), Cr (91.3?545.8 mgkg^?1), Cu (62.9?334.6 mgkg^?1), Co (38.6?81.9 mgkg^?1), Ni (12.4?30.9 mgkg^?1), Cd (6.9?13.2 mgkg^?1), Hg (5.5?10.4 mg kg^?1), and As (2.3?18.6 mgkg^?1). Apart from Ni and As, all the heavy metals recorded concentrations that ranged from 10?900% higher than their respective threshold limit values (TLVs). Heavy metal concentrations from the residential sites were comparatively far lower with only Cr, Cd, and Hg registering concentrations between 65?250% above their TLVs. The cluster with its residential communities is at a serious risk of soil heavy metal toxicity and awareness to this needs to be created as such.     

Characteristic radiation of nitrogen under subnanosecond breakdown in a highly nonuniform electric field near the positive-polarity electrode

Results are presented from experimental studies of elevated-pressure diffuse discharge in a highly nonuniform electric field. It is shown that, in discharges in nitrogen and air, the characteristic radiation (the K-line of nitrogen) is generated at the positive polarity of the electrode with a small curvature radius. X-ray bremsstrahlung from the anode was detected in a discharge in atmospheric-pressure air at a 12-kV amplitude of the incident voltage pulse.     

Dynamic mechanical properties of the tissue-engineered matrix associated with individual chondrocytes

The success of cell-based tissue engineering approaches in restoring biological function will be facilitated by a comprehensive fundamental knowledge of the temporal evolution of the structure and properties of the newly synthesized matrix. Here, we quantify the dynamic oscillatory mechanical behavior of the engineered matrix associated with individual chondrocytes cultured in vitro for up to 28 days in alginate scaffolds. The magnitude of the complex modulus (|E*|) and phase shift (δ) were measured in culture medium using Atomic Force Microscopy (AFM)-based nanoindentation in response to an imposed oscillatory deformation (amplitude ～5 nm) as a function of frequency (f=1–316 Hz), probe tip geometry (2.5 μm radius sphere and 50 nm radius square pyramid), and in the absence and presence of growth factors (GF, insulin growth factor-1, IGF-1, and osteogenic protein-1, OP-1). |E*| for all conditions increased nonlinearly with frequency dependence approximately f^1/2 and ranged between ～1 and 25 kPa. This result, along with theoretical calculations of the characteristic poroelastic relaxation frequency, f_p, (～50–90 Hz) suggested that this time-dependent behavior was governed primarily by fluid flow-dependent poroelasticity, rather than flow-independent viscoelastic processes associated with the solid matrix. |E*(f)| increased, (f) decreased, and the hydraulic permeability, k, decreased with time in culture and with growth factor treatment. This trend of a more elastic-like response was thought to be associated with increased macromolecular biosynthesis, density, and a more mature matrix structure/organization.     

Hybrid MD-Nernst Planck model of α-hemolysin conductance properties

Motivated by experiments in which an applied electric field translocates polynucleotides through an α-hemolysin protein channel causing ionic current transient blockade, a hybrid simulation model is proposed to predict the conductance properties of the open channel. Time scales corresponding to ion permeation processes are reached using the Poisson–Nernst–Planck (PNP) electro-diffusion model in which both solvent and local ion concentrations are represented as a continuum. The diffusion coefficients of the ions (K⁺ and Cl^?) input in the PNP model are, however, calculated from all-atom molecular dynamics (MD). In the MD simulations, a reduced representation of the channel is used. The channel is solvated in a 1?M KCl solution, and an external electric field is applied. The pore specific diffusion coefficients for both ionic species are reduced 5–7 times in comparison to bulk values. Significant statistical variations (17–45%) of the pore-ions diffusivities are observed. Within the statistics, the ionic diffusivities remain invariable for a range of external applied voltages between 30 and 240?mV. In the 2D-PNP calculations, the pore stem is approximated by a smooth cylinder of radius ～9?Å with two constriction blocks where the radius is reduced to ～6?Å. The electrostatic potential includes the contribution from the atomistic charges. The MD-PNP model shows that the atomic charges are responsible for the rectifying behaviour and for the slight anion selectivity of the α-hemolysin pore. Independent of the hierarchy between the anion and cation diffusivities, the anionic contribution to the total ionic current will dominate. The predictions of the MD-PNP model are in good agreement with experimental data and give confidence in the present approach of bridging time scales by combining a microscopic and macroscopic model.     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Cat Heart Muscle in Vitro : III. The extracellular space

The "osmotic gradient" method, an intracellular microelectrode technique for determining whether an uncharged, water-soluble molecule enters cells or remains extracellular, is described. Using this method, a series of carbohydrates of graded molecular size were examined. In cat papillary muscles mannitol, molecular radius 4.0 Å, remained extracellular while arabinose, molecular radius 3.5 Å entered the cells. Measurement of the simultaneous uptake of H³-mannitol and C¹⁴-inulin showed that mannitol equilibrates with 40 per cent of total water in 1 hour, after which the mannitol space does not further increase. By contrast, inulin, molecular radius ~15 Å, equilibrates with 24 per cent of total water in 1 hour; thereafter the inulin space continues to increase very slowly. The intracellular K concentrations are significantly higher and the intracellular Na and Cl concentrations significantly lower when mannitol rather than inulin is used to measure the extracellular space. The intracellular Cl concentration determined with Cl³⁶ or Br⁸² is significantly higher than that calculated from the membrane potential assuming a passive Cl distribution. In addition, it is shown that choline enters and is probably metabolized by the cells of papillary muscle.     

Comprehensive analysis of the roles of ‘black’ and ‘gray’ clusters in structure and function of rat β-parvalbumin

Recently we found two highly conserved structural motifs in the proteins of the EF-hand calcium binding protein family. These motifs provide a supporting scaffold for the Ca²⁺ binding loops and contribute to the hydrophobic core of the EF-hand domain. Each structural motif forms a cluster of three amino acids called cluster I (‘black’ cluster) and cluster II (‘grey’ cluster). Cluster I is much more conserved and mostly incorporates aromatic amino acids. In contrast, cluster II includes a mix of aromatic, hydrophobic, and polar amino acids. The ‘black’ and ‘gray’ clusters in rat β-parvalbumin consist of F48, A100, F103 and G61, L64, M87, respectively. In the present work, we sequentially substituted these amino acids residues by Ala, except Ala100, which was substituted by Val. Physical properties of the mutants were studied by circular dichroism, scanning calorimetry, dynamic light scattering, chemical crosslinking, and fluorescent probe methods. The Ca²⁺ and Mg²⁺ binding affinities of these mutants were evaluated by intrinsic fluorescence and equilibrium dialysis methods. In spite of a rather complicated pattern of contributions of separate amino acid residues of the ‘black’ and ‘gray’ clusters into maintenance of rat β-parvalbumin structural and functional status, the alanine substitutions in the cluster I cause noticeably more pronounced changes in various structural parameters of proteins, such as hydrodynamic radius of apo-form, thermal stability of Ca²⁺/Mg²⁺-loaded forms, and total energy of Ca²⁺ binding in comparison with the changes caused by amino acid substitutions in the cluster II. These findings were further supported by the outputs of computational analysis of the effects of these mutations on the intrinsic disorder predisposition of rat β-parvalbumin, which also indicated that local intrinsic disorder propensities and the overall levels of predicted disorder were strongly affected by mutations in the cluster I, whereas mutations in cluster II had less pronounced effects. These results demonstrate that amino acids of the cluster I provide more essential contribution to the maintenance of structuraland functional properties of the protein in comparison with the residues of the cluster II.     

Formation of nonquasineutral vortex plasma structures with a zero net current

A nonquasineutral vortex structure with a zero net current is described that arises as a result of electron drift in crossed magnetic and electric fields, the latter being produced by charge separation on a spatial scale of about the magnetic Debye radius r _B = |B|/(4πen _e ). In such a structure with a radius of r ～ r _B , the magnetic field is maintained by a drift current on the order of the electron Alfvén current J _Ae = m _e c ³/(2e) and can become as strong as B ? m _e c ²/(er). Estimates show that, in a plasma with a density of n _e = 10²¹?10²³ cm^?3 and with nonzero electron vorticity driven by high-power laser radiation on a time scale on the order of θ _pe ^?1 , magnetic fields with a strength of B ～ 10⁸?10⁹ G are generated on micron and submicron scales. The system with closed current that is considered in the present paper can also serve as a model of hot spots in the channel of a Z-pinch.     

Do cluster roots of Hakea actities (Proteaceae) acquire complex organic nitrogen?

Although there has been speculation that cluster roots play a role in plant nitrogen (N) acquisition there have been few experimental studies, demonstrating this. We grew the subtropical wet heathland plant Hakea actities in sand and in axenic vermiculite-sand cultures to investigate its use of different N sources. Seedlings produced greater quantities of cluster roots when grown with NO₃ ^–, glutathione or protein as N sources than with NH₄ ⁺, glutamine or without N addition, suggesting that N source influences cluster root initiation and development. Axenically grown seedlings acquired more N when grown with 4.5 mM than with 0.5 mM glutathione or protein as N sources suggesting that seedlings are able to assimilate complex organic N. However, control seedlings that did not receive N other than seed storage N (approximately 0.2 mg N) acquired 2 mg N from an unknown source, so that data are not unequivocal. Peptidase activity in extracts derived from non-axenic cluster root tissue changed with age of cluster roots. Developing and mature cluster roots had higher peptidase activity than young and senescing cluster roots. To determine whether peptidases are associated with the outer surface of cluster roots, entire cluster roots were gently centrifuged and the resulting solution analysed for peptidase activity using gelatine-containing PAGE. Different peptidases were active at different times of cluster root development, suggesting that plant or microbially derived peptidases could play a role in organic N acquisition by cluster roots. Roots and cluster roots expressed a putative amino acid transporter (HaAAT4-1) and peptide transporter (HaPepT1) as determined by northern blot analysis. Expression of HaPepT1 in cluster roots increased throughout cluster root development although further studies need to confirm this.     

A multiscale model for plant invasion through allelopathic suppression

In the present paper, we propose and study by numerical simulations a multiscale model for plant invasion based on allelopathic suppression in a homogeneous environment. The negative effects on seed production and germination, establishment and mortality of native plants generated by the root-secreted alien phytotoxin constitute the basic mechanism contributing to invasiveness. We obtained the invasion patterns, their success probabilities, the time evolution of plant populations, the gyration radius and the border roughness of the invaded region. As an important result, it was observed that, in addition to the phytotoxin nature (synthesis and degradation rates, diffusivity and phytotoxic threshold), invasive patterns and invasion success depend on the kind of native plants present in the area. In fact, both success and invasion speed decrease in the presence of resistant native plants. Also, self-affine invasion fronts are smooth (Hurst exponent H = 1) in the absence of resistant plants, but are rough (H ≠ 1) on the contrary. Furthermore, if the resistant native species are randomly distributed on the landscape, the invasion front exhibits long-range correlations (H ～ 0.76), while its border is anti-correlated (H ～ 0.20), if resistant plants are distributed in patches. Finally, the cluster size distribution functions of resistant plants are exponentials with characteristic cluster sizes increasing in time.