Narrow Results

The LM2990-integrated circuit family was among the first low-dropout voltage regulators to use a coupling diode to reduce a quiescent current. In certain conditions, the coupling diode, connected between the output terminal and the driver transistor collector contact, activates to supply the serial power transistor base current from the load. Nonetheless, an indirect characterization of the serial NPN transistor was affected, making it difficult to estimate its forward emitted current gain and a base current as a function of the absorbed total ionizing dose. The original SPICE simulation model had some limitations with generating the faithful simulation of radiation effects in samples supplied with a non-ideal voltage source. Therefore, a novel four-step computer simulation method was developed to specify bias and load conditions when the coupling diode reaction would not negatively affect the characterization of the serial power transistor. The previously reported method for estimating the serial transistor base current could be successfully used for dropout voltages that slightly exceed three equivalent diode voltage drops (that is, 2.4V) at the base-emitter junctions of the output amplifier transistors.

This paper reports on an attempt to investigate how much the sensitivity in PIXE analysis could be improved by optimization of the experimental procedure. The composition and origin of the spectral background in proton excitation of thin plastic foils were studied. It was found that the background could be reduced by good collimation of the beam and efficient shielding of the detector. Minimum detection limits of the order of 0.05–0.2 ppm were obtained. Further improvement with detection limits in the range 0.02–0.03 ppm was achieved by using 5 MeV α-particles for excitation.

The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in X-ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from Refs. 1 and 2 using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in numerical simulation of relativistic tori and spiral waves on the accretion disk. The results of these different dynamical structures on the accretion disk responsible for QPOs are discussed in detail.

From its invention in 1997, the Gas Electron Multiplier (GEM) has been applied in nuclear and high energy physics experiments. Over time however, other applications have also exploited the favorable properties of GEMs. The use of GEMs in these applications will be explained in principle and practice.

This paper reviews applications in research, beam instrumentation and homeland security. The detectors described measure neutral radiations such as photons, x-rays, gamma rays and neutrons, as well as all kinds of charged radiation. This paper provides an overview of the still expanding range of possibilities of this versatile detector concept.

The Pauli Exclusion Principle is a basic principle of Quantum Mechanics, and its validity has never been seriously challenged. However, given its fundamental standing, it is very important to check it as thoroughly as possible. Here we describe the VIP (VIolation of the Pauli exclusion principle) experiment, an improved version of the Ramberg and Snow experiment (E. Ramberg and G. Snow, Phys. Lett. B238, 438 (1990)); VIP has just completed the installation at the Gran Sasso underground laboratory, and aims to test the Pauli Exclusion Principle for electrons with unprecedented accuracy, down to β²/2 ≈ 10^-30 - 10^-31. We report preliminary experimental results and briefly discuss some of the implications of a possible violation.

In almost a decade of operations, Chandra has observed and discovered the X-ray counterparts of several tens of extragalactic radio jets, with a variety of morphologies and SEDs. Here we take a fresh approach and assume that we do not know their relationship. We then search for phenomenological trends. While admittedly naive, this perspective allow us to start identifying key quantities towards a large-scale jet "unitarian view", just as was previously done for their compact, pc-scale cousins, the blazars. Similarly to the latter, we find that key parameters governing the properties of Chandra jets are their powers and the mass flux, the latter parameterizing the jet interaction with the ambient gas.

All galaxies beyond the Magellanic clouds with detected H₂O maser emission so far are investigated and their X-ray observations are collected in detail to probe the X-ray properties of this special kind of galaxies. The soft excess and the strong iron emission line are commonly presented in their X-ray spectrum. Similar to the spectra of normal Seyfert 2 galaxies, the X-ray soft components are usually explained well by two alternative models or their combination: the absorbed power law model and the thermal emission model. The hard X-ray continua are usually flat, which should be caused by the increase of the reflection component, with the increase of the absorbing material density. Modeling their X-ray spectra shows that high absorbing column density is prevalent in our H₂O megamaser host AGNs. Further, we investigate a possible relation between the iron line emission and the nuclear X-ray emission. It shows no significant correlation between the equivalent width (EW) of the neutral FeK_α emission line (~ 6.4 keV) and the intrinsic nuclear X-ray luminosity. However, one trend appears clearly — the EW of the iron line decreases with the increase of the observed X-ray luminosity for our H₂O maser galaxies. We also estimate the accretion rate of H₂O maser host AGNs and the results show that maser galaxies may have a higher accretion rate than nonmaser Seyfert galaxies. In addition, possible relations between the EW of the iron line with the accretion rate and the central black hole mass are investigated and no significant trend of correlation can be found between them.

M 87 is the first and brightest radio galaxy detected in the TeV regime. It is the closest extragalactic object showing variability and the only one that does not have its jet pointing toward the line of sight. The structure of the M 87 jet is spatially resolved in X-ray, optical and radio observations. Time correlation between the TeV flux and emission at other wavelengths provides a unique opportunity to localize the VHE emission process occurring in active galaxy nuclei. For 10 years, M87 has been monitored in the TeV band by imaging air Cherenkov telescopes (IACT) as well as in X-ray, optical and radio bands. In 2008, the three main IACTs, H.E.S.S./MAGIC/VERITAS, coordinated their observations in a joint campaign. In February, high TeV activities with rapid flares have been detected. Contemporaneously, M 87 was observed with high resolution instruments in the X-ray (Chandra) and Radio band (VLBA).

Recent monitoring of the quiescent thermal emission from NSs in low mass X–ray binaries (LMXBs) after active periods (bursts) opened a new view to the physics of dense matter. Theoretical modeling of the thermal relaxation of the crust may be used to establish constraints on the thermal conductivity of matter, depending on the accretion rate. We present here cooling curves obtained from numerical simulations that fit the light curves for two sources (KS 1731-260, MXB 1659-29). We estimate the model parameters (accretion rate, thermal conductivity) that match the data and compare our results with previous constraints of neutron star crust properties in LMXBs.

Intermediate-mass black holes (IMBHs), with masses in the range $100$–$10^6$M${}_{\odot }$, are the link between stellar-mass BHs and supermassive BHs (SMBHs). They are thought to be the seeds from which SMBHs grow, which would explain the existence of quasars with BH masses of up to 10${}^{10}$M${}_{\odot }$ when the Universe was only 0.8 Gyr old. The detection and study of IMBHs has thus strong implications for understanding how SMBHs form and grow, which is ultimately linked to galaxy formation and growth, as well as for studies of the universality of BH accretion or the epoch of reionization. Proving the existence of seed BHs in the early Universe is not yet feasible with the current instrumentation; however, those seeds that did not grow into SMBHs can be found as IMBHs in the nearby Universe. In this review, I summarize the different scenarios proposed for the formation of IMBHs and gather all the observational evidence for the few hundreds of nearby IMBH candidates found in dwarf galaxies, globular clusters, and ultraluminous X-ray sources, as well as the possible discovery of a few seed BHs at high redshift. I discuss some of their properties, such as X-ray weakness and location in the BH mass scaling relations, and the possibility to discover IMBHs through high velocity clouds, tidal disruption events, gravitational waves, or accretion disks in active galactic nuclei. I finalize with the prospects for the detection of IMBHs with up-coming observatories.

We present the first results obtained in the elaboration of a complete model of a microquasar where the donor star is from Population III. These stars do not produce stellar winds so we consider that the mass loss is due exclusively to matter overflowing the Roche lobe towards the compact object, a maximally rotating black hole. The rate of accretion is extremely super-Eddington, with an intense mass loss from the system in the form of winds and jets. We calculate the relativistic particle content of the jet and the corresponding spectral energy distribution (SED) considering a lepto-hadronic model. Prospects for the cosmological implications of these objects are briefly discussed.

EUROPE – Avastin + Metformin = Drastic reduction in skin cancer.

EUROPE – Skin barrier puzzle solved.

EUROPE – Ageing population could boost economy.

EUROPE – Social amoeba replace animals in Bipolar Disorder research.

JAPAN – Rogue DNA plays key role in heart failure.

JAPAN – New photonics technology to spot and help cure diseases earlier.

JAPAN – Researchers at University of Bonn convert skin and umbilical cord cells directly into nerve cells.

SINGAPORE – IBN's 'Fish and Chips' may help accelerate drug discovery.

USA – Non-cancerous brain tumors linked to frequent dental X-rays.

USA – New cellular mechanism against viral infections uncovered.

USA – Study shows unified process of evolution in bacteria and sexual eukaryotes.

USA – Sugar production switch in liver may offer target for new diabetes therapies.

USA – Dengue changes gene activity, function of mosquito salivary glands.

USA – ORNL, Yale take steps toward fast, low-cost DNA sequencing device.

USA – Normal tissue cells have "personal space" issues.

USA – Scientists discover key enzymes that uncross chromosomes.

USA – New Brain-Machine Interface Moves Paralyzed Hand.

USA – Researchers Find Evidence of Banned Antibiotics in Poultry Products.

Tests have been performed on the high sensitive (HS) GAFChromic film to evaluate its densitometric response to external X-rays (photon beam). Several 2 cm by 2 cm pieces of HS and MD-55-2 GAFChromic films were prepared and irradiated for sensitivity comparison, and X-rays energy dependence study. The optical densities of three irradiated pieces of HS film were measured as a function of time to establish the time taken for the optical density to stabilize. The densitometric sensitivity curves comparison showed that the HS film is twice as sensitive as its predecessor, MD-55-2, more spatially uniform and dosimetric measurements can be made with high precision. Its sensitivity is independent of 6 MV and 15 MV X-ray beam energies and its optical density is stable after about 36 hours post-irradiation time.

It is important to deliver radiation to treatment targets with accuracy. Typically, patients are positioned using marks on the surface of the skin. However, without imaging procedures, there is no information about the location of mobile internal organs and targets. The use of implanted radiopaque markers can help localize internal target organs using imaging modalities. Quality assurance procedures have been performed on commercially available spiral gold markers to determine their location and image quality. The results obtained from different, least essential imaging modalities employed in radiation therapy showed that these markers are not as clearly visible on radiographs as compared to the modalities with electronic output formats. The image quality was also poorer on megavoltage as compared to kilovoltage X-ray imaging modalities.

Cytoskeleton plays a central role in many cellular processes, such as migration, adhesion and proliferation. Alterations of its structural properties are commonly associated with different diseases (malignancy, cardiac hypertrophy, etc.). In this work, we studied the effects of X-radiations on cytoskeleton architecture of two cell lines: BALBc/3T3 and Simian virus 40-transformed BALBc/3T3 (SVT2) cells. In agreement with the current literature, we observed reduced adhesion and increased motility of SVT2 cells respect to non-transformed BALBc/3T3. In addition, we showed that two different doses of X-rays (1 and 2 Gy) increased cell-dish adhesiveness and reduced cell proliferation and cell motility of transformed cells, whereas minor effects were measured on the normal counterpart. These results suggested that low doses or fractioning of X-rays may have a normalization effect on the investigated parameters for the transformed cell phenotype.

The Pauli Exclusion Principle (PEP) represents one of the fundamental principles of the modern physics and our comprehension of the surrounding matter is based on it. Even if today there are no compelling reasons to doubt its validity, it still spurs a lively debate on its limits, as testified by the abundant contributions found in the literature and in topical conferences. We present a method of searching for possible small violations of PEP for electrons, through the search for "anomalous" X-ray transitions in copper atoms, produced by "fresh" electrons which can decay in a Pauli-forbidden transition to the 1s level, already occupied by two electrons. The VIP Experiment has the scientific goal to improve by four orders of magnitude the present limit on the probability of PEP violation for electrons, bringing it into the 10^-30–10^-31 region. Preliminary results, together with future plans, are presented.

The Pauli exclusion principle (PEP) and, more generally, the spin-statistics connection, are at the very basis of our understanding of matter, life and Universe. The PEP spurs, presently, a lively debate on its possible limits, deeply rooted in the very foundations of Quantum Mechanics. It is, therefore, extremely important to test the limits of its validity. The Violation of the PEP (VIP) experiment established the best limit on the probability that PEP is violated by electrons, using the method of searching for PEP forbidden atomic transitions in copper. We describe the experimental method, the obtained results, and plans to go beyond the actual limit by upgrading the experimental apparatus. We discuss the possibility of using a similar experimental technique to search for X-rays as a signature of the spontaneous collapse of the wave function predicted by continuous spontaneous localization (CSL) theories.

By performing X-rays measurements in the underground laboratory of Gran Sasso, LNGS-INFN, we test a basic principle of quantum mechanics: the Pauli exclusion principle (PEP). In the future, we aim to use a similar experimental technique to search for X-rays as a signature of the spontaneous collapse of the wave function predicted by continuous spontaneous localization theories. We present the achieved results of the VIP experiment and the future plans to gain two orders of magnitude in testing PEP with the recently VIP2 setup installed at Gran Sasso.

By performing X-ray measurements in the “cosmic silence” of the underground laboratory of Gran Sasso, LNGS-INFN, we test a basic principle of quantum mechanics: the Pauli Exclusion Principle (PEP) for electrons. We present the achieved results of the VIP experiment and the ongoing VIP2 measurement aiming to gain two orders of magnitude improvement in testing PEP. X-ray emission can also be used to put strong constraints on the parameters of the Continuous Spontaneous Localization Model, which was introduced as a possible solution to the measurement problem in Quantum Mechanics. A Bayesian analysis of the data collected by IGEX will be presented, which allows to exclude a broad region of the parameter space which characterizes this model.

This discussion about diagnostic tests for cancer incorporates a powerful branch of Physics namely X-ray diffraction. Although this technique was used to solve the DNA structure using the X-ray diffraction pictures of Rosalind Franklin,¹ and the structure of vitamin B12 by Dorothy Hodgkin² and hosts of other medical related structures, it is poorly understood by the general medical profession and the community at large. To the nonphysicist the patterns appear to have no relation to the results produced. It might as well be written in Greek. The well-known quote of Poincaré, the famous French mathematician and scientist, in 1885 comes to mind: "Science is built up with facts as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house."

In order therefore to build a true understanding of this powerful technique it is necessary to build a firm understanding of the basic facts about this technique, so that the final results will be clear to all, as they will be held up by a firm house of knowledge. So let us take up the first stone.