Low-energy Effects Research Articles

Low-energy D-wave effects in neutral pion photoproduction

The contribution of D waves to physical observables for neutral pion photoproduction in the near threshold region is studied. Heavy Baryon Chiral Perturbation Theory to one loop, and up to O(q4), is used to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. It is found that the inclusion of D waves is necessary to extract the E0+ multipole reliably from present and forthcoming data and to assess the low-energy constants of Chiral Perturbation Theory. Arguments are presented demonstrating that F-wave contributions are negligible in the near-threshold region.

Lorentz Violation: Motivation and New Constraints

We review the main theoretical motivations and observational constraints on Planck scale–suppressed violations of Lorentz invariance. After introducing the problems related to the phenomenological study of quantum gravitational effects, we discuss the main theoretical frameworks within which possible departures from Lorentz invariance can be described. In particular, we focus on the framework of effective field theory, describing several possible ways of including Lorentz violation therein and discussing their theoretical viability. We review the main low-energy effects that are expected in this framework. We discuss the current observational constraints on such a framework, focusing on those achievable through high-energy astrophysics observations. In this context, we present a summary of the most recent and strongest constraints on quantum electrodynamics with Lorentz-violating nonrenormalizable operators. Finally, we discuss the status of the field and its future perspectives.

POLEMIC NOTES ON IR PERTURBATIVE QUANTUM GRAVITY

Quantum gravity is an important and to great extent unsolved problem. There are many different approaches to the quantization of the metric field, both perturbative and nonperturbative. The current situation in the perturbative quantum gravity is characterized by a number of different models, some of them well elaborated but no one perfect nor mathematically neither phenomenologically, mainly because there are no theoretically derived observables which can be experimentally measured. A very interesting one is an effective approach which separates the low-energy quantum effects from the UV sector. In this way one can calculate quantities which are potentially relevant for establishing certain universal features of quantum gravity. In this presentation we give a polemic consideration of the effective approach to the infrared quantum gravity. We question the validity of the recent results in this area and also discuss how one can check the alleged universality of the effective approach.

Effects of heat treatment processes on microstructure and properties of 2·25Cr–1Mo–0·25V HSLA steels

In the present paper, the effects of the heat treatment processes with two conditioning treatments and four quenching–tempering processes on the mechanical properties of 2·25Cr–1Mo–0·25V high strength low alloyed (HSLA) steel are investigated. The results show that the conditioning treatments have obvious effects on the low temperature impact energy but little effect on the tensile strength. The elevation of the final austenitising temperature increases the strength, whereas it results in the decrease in the low temperature impact energy due to the coarse microstructure. The results of the fracture surfaces analysis further make sure that the fracture surfaces of tensile specimens all exhibit ductile characters with a lot of dimples. However, the fracture surfaces of impact specimens exhibit two typical fracture characters, i.e. the ductile and brittle fracture surface corresponding to the fine and coarse microstructures respectively. In addition, the elongation and reduction in area seem to be insensitive to the heat treatments. Meanwhile, the impact fracture mode is more sensitive to the grain size and not to the low temperature impact energy.

Low-energy Ion Beam Biotechnology at Chiang Mai University

AbstractMeV-ion beam has long been applied to biology research and applications for many decades as highly energetic ions are undoubtedly able to interact directly with biology molecules to cause changes in biology. However, low-energy ion beam at tens of keV and even lower has also 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 since the ion range is so short that the ions can hardly directly interact with the key biological molecules for the changes. This talk 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 investigations 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.

Study on the decay mechanisms of surface plasmon coupling features with a light emitter through time-resolved simulations

The transient behaviors of the dipole coupling with surface plasmon (SP) features in an Ag/dielectric-interface grating structure in order to understand the characteristics of those dipole-coupling features are demonstrated. In particular, the major decay mechanisms of those coupling features can be identified. For comparison, the time-resolved behaviors of the resonant surface plasmon polariton (SPP) coupling feature on a flat interface are also illustrated. Among the three major grating-induced SP-dipole coupling features, two of them are identified to be localized surface plasmons (LSPs). The third one is a grating-assisted SPP, which shows two decay components, corresponding to the first stage of SPP in-plane propagation and the second stage of coupling system decay. In all the dipole coupling features, metal dissipation can dominate the energy relaxation process, depending on the assumption of damping factor. All the dissipation rates are proportional to the assumed damping factor in the Drude model of the metal. The dissipation rates of the LSP and resonant SPP features are about the same as the damping rate, implying their local electron oscillation natures. The dissipation rate of the grating-assisted SSP feature is consistent with theoretical calculation. In the LSP features under study, dielectric-side emission is prominent. The coupled energy in the grating-assisted SPP feature can be efficiently stored in the coupling system due to its low emission efficiency and effective energy confinement through grating diffraction.

Water Repellency on a Fluorine-Containing Polyurethane Surface: Toward Understanding the Surface Self-Cleaning Effect

Surface geometrical microstructure and low surface free energy are the two most important factors for a self-cleaning surface. In this study, multiform geometrical microstructured surfaces were fabricated by casting and electrospinning polyurethanes with and without low surface energy segments. The effect of low surface energy on water repellency was evaluated. Low surface energy seems to make a more significant contribution to the static wetting behavior than do dynamic properties such as the improvement of sliding behavior. Sucking disk behavior was brought forward to explain the pinning state of a water droplet on hydrophobic surfaces with high water contact angles (>150 degrees ). A better understanding of the relationship between the static contact angle and the dynamic sliding property was provided.

Low-energy rescattering effects in photoionization

The Coulomb-corrected KFR theory is applied to the analysis of the photoemission spectra of hydrogen atoms irradiated by a high intensity laser field. We report the observation of peaks in the ionization signals obtained for intensities in the tunnelling regime and show that their positions are intensity-independent. The interpretation of this result by means of the Coulomb-corrected KFR theory leads to the conclusion that the above features of the photoionization spectra are due to low-energy rescattering and channel closing effects. Our investigation of the electron momentum distributions suggests that low-energy photoelectrons are created in attosecond pulses.

Sol–gel coating of cellulose fibres with antimicrobial and repellent properties

Multifunctional, water and oil repellent and antimicrobial finishes for cotton fibres were prepared from a commercially available fluoroalkylfunctional water-born siloxane (FAS) (Degussa), nanosized silver (Ag) (CHT) and a reactive organic–inorganic binder (RB) (CHT). Two different application procedures were used: firstly, one stage treatment of cotton fabric samples by FAS sol (i), as well as by a sol mixture constituted from all three precursors (Ag–RB–FAS, procedure 1S) (ii), and secondly, two stage treatment of cotton by Ag–RB sol and than by FAS sol (Ag–RB + FAS, procedure 2S) (iii). The hydrophobic and oleophobic properties of cotton fabrics treated by procedures (i)–(iii) before and after consecutive (up to 10) washings were established from contact angle measurements (water, diiodomethane and n-hexadecane) and correlated with infrared and XPS spectroscopic measurements. The results revealed that even after 10 washing cycles cotton treated with Ag–RB + FAS (2S) retained an oleophobicity similar to that of the FAS treated cotton, while the Ag–RB–FAS (1S) cotton fibres exhibited a loss of oleophobicity already after the second washing, even though fluorine and C–F vibrational bands were detected in the corresponding XPS and IR spectra. The antibacterial activity of cotton treated by procedures (i)–(iii) was tested by its reduction of the bacteria Escherichia coli and Staphylococcus aureus following the AATCC 100-1999 standard method and EN ISO 20743:2007 transfer method. The reduction in growth of both bacteria was nearly complete for the unwashed Ag–RB and Ag–RB–FAS (S1), but for the unwashed Ag–RB + FAS (S2) treated cotton no reduction of S. aureus and 43.5 ± 6.9% reduction of E. coli was noted. After the first washing, the latter two finishes exhibited nearly a complete reduction of E. coli but for the Ag–RB treated cotton the reduction dropped to 88.9 ± 3.4. None of the finishes retained antibacterial properties after 10 repetitive washings. The beneficial and long-lasting low surface energy effect of FAS finishes in the absence of Ag nanoparticles, which led to the “passive” antibacterial properties of FAS treated cotton fabrics, was established by applying the EN ISO 20743:2007 transfer method. The results revealed a reduction in bacteria of about 21.9 ± 5.7% (FAS), 13.1 ± 4.8% (Ag–RB–FAS (S1)) and 41.5 ± 3.7% (Ag–Rb + FAS (S2)), while no reduction of the growth of bacteria was observed for cotton treated with Ag nanoparticles after 10 repetitive washings. The physical properties (bending rigidity, breaking strength, air permeability) of finished cotton samples were determined, and showed increased fabric softness and flexibility as compared to the Ag–RB treated cotton, but a slight decrease of breaking strength in the warp and weft directions, while air permeability decreased for all type of finishes.

Implantation effects of low energy H and D ions in germanium at −120 °C and room temperature

Germanium was implanted with 5keV H and D ions at −120°C or room temperature and thermally annealed in several steps. The samples were analysed at various stages by atomic force microscopy, ion channeling and Raman spectroscopy of Ge-H/D local vibration modes. The results are discussed in comparison with those in the well studied silicon. In general, the evolution of the different types of defects, in germanium at a given temperature, tends to be similar to that of the corresponding defects in silicon at 100–300°C higher temperature. However, the behaviour of the defects detected by ion channeling (interstitials, lattice distortions) often appears unrelated to the chemical evolution measured by Raman scattering and to the temperature and isotope dependence of blistering.

Low energy effects of neutrino masses

While all models of Majorana neutrino masses lead to the same dimension five effective operator, which does not conserve lepton number, the dimension six operators induced at low energies conserve lepton number and differ depending on the high energy model of new physics. We derive the low-energy dimension six operators which are characteristic of generic Seesaw models, in which neutrino masses result from the exchange of heavy fields which may be either fermionic singlets, fermionic triplets or scalar triplets. The resulting operators may lead to effects observable in the near future, if the coefficients of the dimension five and six operators are decoupled along a certain pattern, which turns out to be common to all models. The phenomenological consequences are explored as well, including their contributions to μ→eγ and new bounds on the Yukawa couplings for each model.

An Analysis of the Effects of Low-Energy Electron Irradiation of AlGaN/GaN HFETs

The effects of low energy (0.45 MeV) electron radiation on the gate and drain currents of Al0.27Ga0.73N/GaN HFETs are investigated using IV and CV measurements. Following irradiation, the gate and drain currents increase at low temperatures and reach a saturation level. The gate leakage currents do not fully account for the drain current increase. Following a room temperature anneal, the gate and drain currents return to pre-irradiation levels. These results are explained by the buildup of positive charge in the AlGaN layer at low temperature and traps formed via a complexing precursor in the AlGaN layer near the interface. The positive charge increases the carrier concentration in the 2DEG and hence the drain current. The traps act as trap-assisted-tunneling centers that increase the gate leakage current.

S180 cell growth on low ion energy plasma treated TiO 2 thin films

X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2 eV) argon ion plasma surface modification of TiO 2 thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO 2 in a two-stage hybrid system had increased the proportion of surface states of TiO 2 as Ti 3+. The proportion of carbon atoms as alcohol/ether (C OX) was decreased with increase the RF power and carbon atoms as carbonyl (C O) functionality had increased for low RF power treatment. The proportion of C( O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO 2 surfaces whereas small-localised cell free area can be seen on plasma treated TiO 2 surfaces which may be due to decrease in C( O)OX, increase in C O and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO 2 surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO 2 was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry.

Experimental verification of beam quality in high‐contrast imaging with orthogonal bremsstrahlung photon beamsa)

Since taken with megavoltage, forward-directed bremsstrahlung beams, the image quality of current portal images is inferior to that of diagnostic quality images produced by kilovoltage beams. In this paper, the beam quality of orthogonal bremsstrahlung beams defined as the 90 degrees component of the bremsstrahlung distribution produced from megavoltage electron pencil beams striking various targets is presented, and the suitability of their use for improved radiotherapy imaging is evaluated. A 10 MeV electron beam emerging through the research port of a Varian Clinac-18 linac was made to strike targets of carbon, aluminum, and copper. PDD and attenuation measurements of both the forward and orthogonal beams were carried out, and the results were also used to estimate the effective and mean energy of the beams. The mean energy of a spectrum produced by a carbon target dropped by 83% from 1296 keV in the forward direction to 217 keV in the orthogonal direction, while for an aluminum target it dropped by 77% to 412 keV, and for a copper target by 65% to 793 keV. An in-depth Monte Carlo study of photon yield and electron contamination was also performed. Photon yield and effective energy are lower for orthogonal beams than for forward beams, and the differences are more pronounced for targets of lower atomic number. Using their relatively low effective energy, orthogonal bremsstrahlung beams produced by megavoltage electrons striking low atomic number targets yield images with a higher contrast in comparison with forward bremsstrahlung beams.

Optical and Structural Modifications in Heavy Ion Irradiated Polystyrene

Samples of polystyrene (PS) have been irradiated with 64Cu (50 and 120 MeV) and 12C (70 MeV) ion beams (fluence=1011 to 1013 ions cm−2) in order to study the induced modifications using UV‐VIS and FTIR spectroscopy. UV spectra of irradiated samples reveal that the optical band gap decreases from 4.36 to 1.46 eV in PS. The decrease in optical band gap is more pronounced with the Cu‐ion beam due to high electronic energy loss as compared to the C ion beam. The effect of low energy (50 MeV) Cu ions on the optical properties of PS is larger than that due to high energy (120 MeV) Cu ions. The correlation between the optical band gap and the number of six member carbon rings inside the largest carbon clusters embedded in the network of polystyrene is discussed. FTIR spectra reveal the formation of hydroxyl, alkene, and alkyne groups in the Cu‐ion irradiated PS. Changes in the intensity of the absorption bands on irradiation with C‐ion relative to pristine samples have also been observed and are discussed.

Damaging Effect of Low Energy N+ Implantation on Aspergillus niger Spores

The mutant effects of a keV range nitrogen ion (N+) beam on enzyme-producing probiotics were studied, particularly with regard to the induction in the genome. The electron spin resonance (ESR) results showed that the signal of ESR spectrum existed in both implanted and non-implanted spores, and the yields of free radicals increased in a dose-dependent manner. The ionic etching and dilapidation of cell wall could be observed distinctly through the scanning electron microscope (SEM). The mutagenic effect on genome indicated that N+ implantation could make base mutation. This study provided an insight into the roles low-energy ions might play in inducing mutagenesis of micro-organisms.

Fluoride thin film formation with low optical absorption by gas cluster ion beam assisted deposition

Gas cluster ion beam (GCIB) shows characteristics of low-energy irradiation effect and dense energy deposition. GCIB-assisted deposition is expected to be used for high-quality fluoride film formation, although these films are sensitive to damage by ion irradiation. In this study, LaF3 and MgF2 films were deposited by SF6-GCIB-assisted deposition. When the acceleration voltage was 3–7kV, the deposited LaF3 film had a high packing density, small columnar structure, and very flat surface. The average roughness of the LaF3 film surface was 0.25nm by the surface smoothing effect of the GCIB. The LaF3 film density showed 5.90g/cm3, which was very close to the theoretical density of crystalline LaF3. The refractive index (n) of the LaF3 film increased from 1.62 to 1.72 with an increase in the ion current density. The extinction coefficient (k) was 1×10−3 at a wavelength of 193nm. By the deposition of a thin layer of Al2O3(extinction coefficient: 5×10−3) on the quartz substrate as an interfacial film, a strong adhesive fluoride film was obtained.

Low-energy ion irradiation effects on hydrogen absorption and desorption in carbon nanotubes

Due to their unique structure, which provides a large ratio of surface area to volume, carbon nanotubes (CNTs) may prove to be ideal materials for hydrogen storage. Typically, hydrogen is stored in CNTs by exposure of the material to a high-pressure H 2 atmosphere at various temperatures. The maximum hydrogen concentrations stored following this method and measured using Ion Beam Analysis do not exceed 1 wt.%. Introduction of defects by ion irradiation prior to high-pressure H 2 treatment, offers an alternative method to activate H adsorption and enhance the chemisorption of hydrogen. In this work, a low-energy H − beam at 13.5 keV was used to irradiate single-wall nanotubes (SWNTs) and to produce defects in SWNTs to enhance hydrogen adsorption. Hydrogen desorption measurements are presented, which compare the behavior in irradiated and as-prepared SWNTs after hydrogen storage treatment. These desorption measurements showed a large enhancement of hydrogen desorption for irradiated samples.

MgF 2 and LaF 3 thin film formation with gas cluster ion beam assisted deposition

Gas cluster ion beams (GCIB), containing huge aggregates with several thousands of atoms or molecules, were employed as assist ion beams for fluoride film formation. As gas cluster ions shows low-energy effects, chemical reaction enhancement and strong surface smoothing effects, GCIB-assisted deposition can be a desirable deposition technique for thin film multilayer structures for the ultra-violet region. In this work, SF6-GCIB was employed as the assist ion beam for deposition of fluoride films (MgF 2 and LaF 3). For fluoride films, it had been difficult to use energetic ions during deposition because of damage induced by ion bombardments. With SF 6-GCIB irradiation, the surface roughness of LaF 3 and MgF 2 films decreased with increasing ion current density. From cross-sectional images, the film structure changed from columnar to bulk-like structure with high-dose SF 6-GCIB irradiation.

Low-Energy Irradiation Effects of Gas Cluster Ion Beams

A cluster-ion irradiation system with cluster-size selection has been developed to study the effects of the cluster size for surface processes using cluster ions. A permanent magnet with a magnetic field of 1.2 T is installed for size separation of large cluster ions. Trace formations at HOPG surface by the irradiation with size-selected Ar-cluster ions under acceleration energy of 30 keV were investigated by a scanning tunneling microscopy. Generation behavior of the crater-like traces is strongly affected by the number of constituent atoms (cluster size) of the irradiating cluster ion. When the incident cluster ion is composed of 100 - 3000 atoms, crater-like traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster-ions composed of over 5000 atoms. Such the behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion. To study GCIB irradiation effects against macromolecule, GCIB was irradiated on DNA molecules absorbed on graphite surface. By the GCIB irradiation, much more DNA molecules was sputtered away as compared with the monomer-ion irradiation.