Low-energy Effects Research Articles

Understanding neutrino properties from decoupling right-handed neutrinos and extra Higgs doublets

Low energy effects induced by heavy extra degrees of freedom are suppressed by powers of the large mass scale, thus preserving, if sufficiently heavy, the successes of the Standard Model in describing low energy phenomena. However, as is well known, heavy right-handed neutrinos may play an important role in low energy phenomenology as an explanation of the smallness of neutrino masses. We consider in this paper an extension of the Standard Model by heavy right-handed neutrinos and heavy Higgs doublets and we show, using a renormalization group approach, that this model can simultaneously provide an explanation for the small neutrino masses and for the mild hierarchy observed between the atmospheric and the solar mass splittings, even when the extra degrees of freedom are very heavy. We analyze the necessary conditions to reproduce the oscillation parameters and we discuss possible experimental signatures of this model.

Ion beam modification of biological materials in nanoscale

Ion interaction with biological objects in nanoscale is a novel research area stemming from applications of low-energy ion beams in biotechnology and biomedicine. Although the ion beam applications in biotechnology and biomedicine have achieved great successes, many mechanisms remain unclear and many new applications are to be explored. We have carried out some research on exploring the mechanisms and new applications besides attaining ion beam induction of mutation breeding and gene transformation. In the studies on the mechanisms, we focused our investigations on the direct interaction in nanoscale between ions and biological living materials. Our research topics have included the low-energy ion range in DNA, low-energy ion or neutral beam bombardment effect on DNA topological form change and mutation, low-energy ion or neutral beam bombardment effect on the cell envelope and gene transformation, and molecular dynamics simulation of ultra-low-energy ion irradiation of DNA. In the exploration of new applications, we have started experiments on ion irradiation or bombardment, in the nanoscaled depth or area, of human cells for biomedical research. This paper introduces our experiments and reports interesting results.

Modelling low energy electron and positron tracks for biomedical applications

Purpose: To incorporate the effects of low energy electrons and positrons into radiation interaction models.Materials and methods: The simulation method proposed here was based on experimental and theoretical cross section data and energy loss spectra we have previously derived. After a summary of the main techniques used to obtain reliable input data, the basis of a Low Energy Particle Track Simulation (LEPTS) procedure was established. The programme is specifically designed to describe electron and positron interactions below 10 keV, down to thermal energies.Results: Single electron and positron tracks in water are presented and the possibility of using these results to develop tools for nanodosimetry is discussed.Conclusions: Standard approximations based on high incident energies, such as the Born-Bethe theory, are not suitable to simulate electron and positron tracks below 10 keV. Prior to the inclusion of low-energy effects in a radiation model, an appropriate study is required to determine both the interaction cross sections and the energy loss spectra.

The impact of prostate edema on cell survival and tumor control after permanent interstitial brachytherapy for early stage prostate cancers

Previous studies have shown that procedure-induced prostate edema during permanent interstitial brachytherapy (PIB) can cause significant variations in the dose delivered to the prostate gland. Because the clinical impact of edema-induced dose variations strongly depends on the magnitude of the edema, the temporal pattern of its resolution and its interplay with the decay of radioactivity and the underlying biological processes of tumor cells (such as tumor potential doubling time), we investigated the impact of edema-induced dose variations on the tumor cell survival and tumor control probability after PIB with the 131Cs, 125I and 103Pd sources used in current clinical practice. The exponential edema resolution model reported by Waterman et al (1998 Int. J. Radiat. Oncol. Biol. Phys. 41 1069–77) was used to characterize the edema evolutions previously observed during clinical PIB for prostate cancer. The concept of biologically effective dose, taking into account tumor cell proliferation and sublethal damage repair during dose delivery, was used to characterize the effects of prostate edema on cell survival and tumor control probability. Our calculation indicated that prostate edema, if not appropriately taken into account, can increase the cell survival and decrease the probability of local control of PIB. The magnitude of an edema-induced increase in cell survival increased with increasing edema severity, decreasing half-life of radioactive decay and decreasing photon energy emitted by the source. At the doses currently prescribed for PIB and for prostate cancer cells characterized by nominal radiobiology parameters recommended by AAPM TG-137, PIB using 125I sources was less affected by edema than PIB using 131Cs or 103Pd sources due to the long radioactive decay half-life of 125I. The effect of edema on PIB using 131Cs or 103Pd was similar. The effect of edema on 103Pd PIB was slightly greater, even though the decay half-life of 103Pd (17 days) is longer than that of 131Cs (9.7 days), because the advantage of the longer 103Pd decay half-life was negated by the lower effective energy of the photons it emits (∼21 keV compared to ∼30.4 keV for 131Cs). In addition, the impact of edema could be reduced or enhanced by differences in the tumor characteristics (e.g. potential tumor doubling time or the α/β ratio), and the effect of these factors varied for the different radioactive sources. There is a clear need to consider the effects of prostate edema during the planning and evaluation of permanent interstitial brachytherapy treatments for prostate cancer.

Exploring the foundations of physics in solid state systems at ultra-low energy

The emergence of quantum field theory as a coarse grained effective model grounded on a more fundamental level is often conjectured. The hypothesis is based both on the lack of a unified theory capable to consistently include gravity and on the existence of several known classes of low energy effects in which effective properties emerge on a coarse grained level. Solid state physics presents major examples of emergence. Effective properties of electrons and light in solid state media mimic, through both collective and coarse grained properties, some fundamental characteristics attributed to particles and spacetime. Here, three low energy mechanisms of the solid state physics connected to those properties are considered, with a particular attention to the relevant energy scale: zero mass fermions in graphene, asymptotic freedom in semiconductor quantum dots, and effective curvature of space in negative refractive index metamaterials.

Effect of low energy electron irradiation on optical properties of InGaN/GaN light emitting structures

AbstractThe effect of low energy e‐beam irradiation on the InGaN related cathodoluminescence in the MQW InGaN/GaN LED structures with different number of quantum wells has been studied. It is shown that the e‐beam exposure leads to an increase of emission intensity and to a formation of new blue‐shifted emission bands. It is shown that the changes in the optical properties are determined by the excess carrier injection. The changes observed were associated with the local changes of InGaN content due to In and/or Ga diffusion stimulated by the excess carrier recombination (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Robust determination of effective atomic numbers for electron interactions with TLD-100 and TLD-100H thermoluminescent dosimeters

Lithium fluoride thermoluminescent dosimeters (TLD) are the most commonly implemented for clinical dosimetry. The small physical magnitude of TLDs makes them attractive for applications such as small field measurement, in vivo dosimetry and measurement of out-of-field doses to critical structures. The most broadly used TLD is TLD-100 (LiF:Mg,Ti) and, for applications requiring higher sensitivity to low-doses, TLD-100H (LiF:Mg,Cu,P) is frequently employed. The radiological properties of these TLDs are therefore of significant interest. For the first time, in this study effective atomic numbers for radiative, collisional and total electron interaction processes are calculated for TLD-100 and TLD-100H dosimeters over the energy range 1 keV–100 MeV. This is undertaken using a robust, energy-dependent method of calculation rather than typical power-law approximations. The influence of dopant concentrations and unwanted impurities is also investigated. The two TLDs exhibit similar effective atomic numbers, ranging from approximately 5.77–6.51. Differences arising from the different dopants are most pronounced in low-energy radiative effects. The TLDs have atomic numbers approximately 1.48–2.06 times that of water. The effective atomic number of TLD-100H is consistently higher than that of TLD-100 over a broad energy range, due to the greater influence of the higher- Z dopants on the electron interaction cross sections. Typical variation in dopant concentration does not significantly influence the effective atomic number. The influence on TLD-100H is comparatively more pronounced than that on TLD-100. Contrariwise, unwanted hydroxide impurities influence TLD-100 more than TLD-100H. The effective atomic number is a key parameter that influences the radiological properties and energy response of TLDs. Although many properties of these TLDs have been studied rigorously, as yet there has been no investigation of their effective atomic numbers for electron interactions. The discrepancy between the effective atomic numbers of the TLDs and water is significantly higher than would be indicated by comparing effective atomic numbers calculated via the common – but dubious – power-law method. The mean effective numbers over the full energy range are 6.06, 6.09, 3.34 and 3.37 for TLD-100, TLD-100H, soft tissue and water respectively.

Low-energy Ion Beam Biology Research at Chiang Mai University

Ion beam at energy lower than tens of keV has been found to have significant biological effects on living materials. The finding has led to applications of ion-beam induced mutation and gene transfer. From the theoretical point of view, the low-energy ion beam effects on biology are difficult to understand with the knowledge of high-energy ion irradiation of biological matter since the ion range is so short that the ions can hardly directly interact with the key biological molecules for the changes. This paper introduces interesting aspects of low-energy ion beam biology, including basis of ion beam biotechnology and recent developments achieved in Chiang Mai University in relevant applications such as mutation and gene transfer and investigation on mechanisms involved in the low-energy ion interaction with biological matter such as eV-keV ion beam bombardments of naked DNA and the cell envelopes.

Charge Collection in Power MOSFETs for SEB Characterisation—Evidence of Energy Effects

Charge collection is used as a non-destructive technique to analyze the statistical response of vertical power MOSFETs and their single-event burnout (SEB) rate as a function of the incident ion energy. Two effects are observed at either low or high energy. At low energy, the collected charge significantly decreases because of the limited ion range and energy straggling in the thick epitaxial layer. Because of this limited range effect, using low energy ions for SEB testing can significantly underestimate the SEB rate. At high energy, the presence of thick source bond wires, which partially cover the die area, as typically encountered in power MOSFETs, induce a large shadowing effect. When crossing the bond wires, high energy ions loose energy and can have a higher LET (but still a significant range) when they reach the active die. As a result, they can deposit more charge in the thick sensitive epitaxial layers of the transistors than the primary beam. A significant probability of high collected charge events is then observed at high energy. Contrary to the low energy (range) effect, the shadowing at high energy contributes to overestimating the SEB rate. General rules for the SEB radiation hardness assurance, related to the ion energy versus the power MOSFET voltage rating, are provided to avoid both range and shadowing effects.

Transport in carbon nanotube field-effect transistors tuned using low energy electron beamexposure

We have studied the effect of low energy (30 keV) electron beam exposure on carbonnanotube field-effect transistors, using an electron beam lithography system toprovide spatially controlled dosage. We show that reversible tuning of the transportbehavior is possible when a backgate potential is applied during exposure. n-typebehavior can be obtained by electron beam exposure of a device with positivegate bias, while ambipolar behavior can be obtained via negative gate bias. Theobserved transport behavior is relatively stable in time. We propose possiblemechanisms for the observed phenomena and suggest directions for further research.

Raman study of ion-induced defects inN-layer graphene

Raman scattering is used to study the effect of low energy (90 eV)Ar + ion bombardment in graphene samples as a function of the number of layersN. The evolution of the intensity ratio between the G band (1585 cm − 1) and the disorder-inducedD band (1345 cm − 1) with ion fluence is determined for mono-, bi-, tri- and ∼ 50-layergraphene samples, providing a spectroscopy-based method to study the penetration of these low energyAr + ions in AB Bernal stacked graphite, and how they affect the graphene sheets. The resultsclearly depend on the number of layers. We also analyze the evolution of the overallintegrated Raman intensity and the integrated intensity for disorder-induced versusRaman-allowed peaks.

Toward Screening for Antibiotics with Enhanced Permeation Properties through Bacterial Porins

Gram-negative bacteria are protected by an outer membrane barrier, and to reach their periplasmic target, penicillins have to diffuse through outer membrane porins such as OmpF. Here we propose a structure-dynamics-based strategy for improving such antibiotic uptake. Using a variety of experiments (high-resolution single channel recording, Minimum Inhibitory Concentration (MIC), liposome swelling assay) and accelerated molecular simulations, we decipher the subtle balance of interactions governing ampicillin diffusion through the porin OmpF. This suggests mutagenesis of a hot spot residue of OmpF for which additional simulations reveal drastic changes in the molecular and energetic pathway of ampicillin's diffusion. Inverting the problem, we predict and describe how benzylpenicillin diffuses with a lower effective energy barrier by interacting differently with OmpF. The thorough comparison between the theoretical predictions and the three independent experiments, which were set up to measure the kinetics of transport and biological activity, gives insights on how to combine such different investigation techniques with the aim of providing complementary validation. Our study illustrates the importance of microscopic interactions at the constriction region of the biological channel to control the antibiotic flux through it. We conclude by providing a complete inventory of the channel and antibiotic hot spots and discuss the implications in terms of antibacterial screening and design.

Realization of the exactly solvable Kitaev honeycomb lattice model in a spin-rotation-invariant system

The exactly solvable Kitaev honeycomb lattice model is realized as the low energy effect Hamiltonian of a spin-1/2 model with spin rotation and time-reversal symmetry. The mapping to low energy effective Hamiltonian is exact, without truncation errors in traditional perturbation series expansions. This model consists of a honeycomb lattice of clusters of four spin-1/2 moments, and contains short-range interactions up to six-spin(or eight-spin) terms. The spin in the Kitaev model is represented not as these spin-1/2 moments, but as pseudo-spin of the two-dimensional spin singlet sector of the four antiferromagnetically coupled spin-1/2 moments within each cluster. Spin correlations in the Kitaev model are mapped to dimer correlations or spin-chirality correlations in this model. This exact construction is quite general and can be used to make other interesting spin-1/2 models from spin rotation invariant Hamiltonians. We discuss two possible routes to generate the high order spin interactions from more natural couplings, which involves perturbative expansions thus breaks the exact mapping, although in a controlled manner.

Lifetime Broadening of a Nuclear Magnetic Resonance Peak under Minimal Length Uncertainty Analysis

It is expected that some low energy relics of high energy phenomena may be verified by nowadays experiments, and some phenomenological low energy effects may be explored in solvable models at a level of quantum mechanics in a minimal length scale [1–9]. In literature, the minimal length quantum mechanics have been extensively studied [10, 1, 2]. In this letter we study the possibility of testing minimal length scale via nuclear magnetic resonance spectroscopy taking into account the solution of broadening of a magnetic resonance peak by minimal length uncertainty. One manifestation of the uncertainty principle is the effect of decreasing the lifetime of a nucleus in a given environment on the nuclear magnetic resonance spectrum of the same nucleus or one to which it is coupled. These kinetic effects may have experimental significance by giving rise to spectra whose shift-state values or line widths may be used as a measure, or to spectra which are simplified so that the resonances are more suitable for quantitative measurements. The shifting and merging of spectra by kinetic process may also be used to shift an increasing resonance away from a resonance of interest if the interfering species can be made to undergo rapid exchange. The magnitude of the effect can be estimated from uncertainty principle, ∆E∆t ≥ ~. Since ∆E = ~∆ν and ∆t may be identified with τ , the average lifetime of the excited state in the various exchanging states, the relationship becomes τ∆ν ≈ 1/2π. Thus the magnitude of the rate constant that will give an observable effect will vary for different types of spectrometry, depending on the frequency difference involved. The widest application of this principle has been in nuclear magnetic resonance spectrometry, especially proton NMR. When a system

Surface free energy analysis for bipolar pulsed argon plasma treated polymer films

The effect of low energy (300 eV) argon plasma treatment on the morphology of polycarbonate was studied by means of contact angle measurement, X-ray photoelectron spectroscopy (XPS), Vickers' micro hardness indentation and atomic force microscopy (AFM). The surface free energy (SFE) changes from 38.5 mJ/m2 to 74.9 mJ/m2 on increasing the treatment time and the corresponding contact angle was changed from 63° to 17°, which shows the enhancement in surface adhesion. The XPS analysis shows the increase of the C-O and C=O functional groups upon treatment. The Vickers' micro hardness was studied in the load range 10-500 gf. The micro hardness of the film increases with the treatment time. Atomic force microscopy (AFM) reveals that average surface roughness increases from 7.0 nm to 27.2 nm as treatment time increases.

Intramedullary fixation and proximal femoral fractures: Diversity in use through case reports

Proximal femoral fractures, including intertrochanetric and subtrochanteric with diaphiseal propagation represent a significant challenge in orthopedic surgery, especially in older population. Retrospective analysis of patients, after the application of "Bi Nail (Bioimpianti Inc.) intramedullary nail for fractures and pathological conditions of proximal femur, was done at the Department of Adult Orthopedics, Institute of Orthopedic surgery Banjica, during the three year period. We present patients with complex fractures and pathological conditions (metastasis and pseudoarthrosis) of proximal femur; most of the fractures were result of effects of low energy, and the most common pathological fracture is due to metastasis of breast cancer. The analysis included the technical characteristics and duration of surgery, intraoperative and postoperative complications as well as the coalescence time of fracture healing and postoperative quality of life after rehabilitation. We believe that the described surgical method, although technically demanding, with a variable length duration of surgery and treatment of high risk elderly patients, provides stable fracture fixation with early rehabilitation to improve the quality of life.

Low-energy electrons and X-ray irradiation effects on plasma-polymerized allylamine bioactive coatings for stents

Radiation used in biomedical applications causes chemical changes to biomedical materials. This work is an ex situ simulation of the influence of low-energy electron (LEE) impact and X-ray irradiation on the chemical properties of plasma-polymerized allylamine (PPA) bioactive and biocompatible stent coatings. Preliminary X-ray photoelectron spectroscopy (XPS) results show that PPA coatings oxidize in contact with ambient air by the detection of C–O and C O bonds which are typical of polymer oxidation. Chemical changes after LEE and X-ray irradiation are mainly a loss of oxygen, assuming a surface deoxidizing and not a complete destruction of the surface. XPS survey analyses show that the amine groups remain stable during irradiation. LEE impact measurements by TOF mass spectrometry show that the main ionic losses are H − ions. It appears that CN groups are stable under irradiation and we observe a loss of hydrogen and oxygen as the main chemical modifications. In conclusion, these results suggest that PPA coatings are stable under biomedical radiation, and they can therefore be used for bioactive and biocompatible stent coatings.

Acids and alkali resistant sticky superhydrophobic surfaces by one-pot electropolymerization of perfluoroalkyl alkyl pyrrole

Over the past few years, electropolymerization of semifluorinated monomers like thiophene or pyrrole has been used as a gentle and effective method to generate, in one step, stable superhydrophobic surfaces. The synthetic route mostly involves the coupling reaction between a carboxylic acid and an alcohol, using a carboxy group-activated reagent and a catalyst. As a consequence, the electroformed surfaces present high liquid repellency due to the concomitant effect of roughness and low surface energy. Nevertheless, the ester connector can be cleaved under acidic and basic conditions, preventing its use under a range of environmental conditions. To overcome this drawback, a new perfluoroalkyl alkyl pyrrole has been synthesized, the fluorinated segment being connected to the electropolymerizable part via an alkyl chain, and electropolymerized, leading to surfaces that exhibit a static contact angle with water superior to 150° and no sliding angle, over a wide pH range and with a long lifetime. This represents the first example of a pure conducting polymer surface with sticky superhydrophobicity not only in pure water but also in corrosive solutions such as acids and bases, giving rise to new prospects in practical applications.

Planarization of Bit-Patterned Surface Using Gas Cluster Ion Beams

The planarization of the bit-patterned surface using gas cluster ion beams (GCIBs) was studied. By applying the features of gas cluster ions, such as low-energy irradiation and surface smoothing effects, it is possible to carry out effective smoothing of a patterned surface. We fabricated a dot pattern on the Si substrate as a model structure for bit-patterned media by electron beam lithography and inductive coupled plasma etching. A carbon overcoat covered the Si dots. On Ar-GCIB irradiation at an acceleration voltage of 20 kV, the Si dots with a diameter of 150 nm were planarized. The required ion dose for planarization was 5 times 1014 ions/cm2. The cross-sectional transmission electron microscope images showed that only the carbon overcoat layer was planarized without a change in the structure of Si dots. Etching depth of the overcoat increased linearly with the ion dose, indicating good reproducibility of the method with precise control of residual thickness.

The low-energy ion range in DNA

In fundamental studies of low-energy ion irradiation effects on DNA, calculation of the low-energy ion range, an important basic physical parameter, is often necessary. However, up to now a unified model and approach for range calculation is still lacking, and reported data are quite divergent and thus unreliable. Here we describe an approach for calculation of the ion range, using a simplified mean-pseudoatom model of the DNA target. Based on ion stopping theory, for the case of low-energy (⩽ a few keV) ion implantation into DNA, the stopping falls in the low reduced energy regime, which gives a cube-root energy dependence of the stopping (E1/3). Calculation formulas of the ion range in DNA are obtained and presented to unify the relevant calculations. The upper limits of the ion energy as a function of the atomic number of the bombarding ion species are proposed for the low-energy case to hold. Comparison of the results of this approach with the results of some widely used computer simulation codes and with results reported by other groups indicates that the approach described here provides convincing and dependable results.