Photon Ratio Research Articles

Nuclear Physics Solutions to the Primordial Lithium Problem

The primordial lithium problem is one of the major outstanding issues in the standard model of the Big Bang. Measurements of the baryon to photon ratio in the cosmic microwave background constrain model predictions, giving abundances of 7Li two to four times larger than observed via spectroscopic measurements of metal-poor stars. In an attempt to reconcile this discrepancy, significant effort has been directed at measuring reaction cross sections of light nuclei at astrophysically relevant energies. However, there remain reaction cross sections with large uncertainties, and some that have not yet been measured. Particularly relevant are those involving the destruction of 7Be, a progenitor of 7Li. Key issues that can be improved by nuclear physics input will be highlighted, and the applicability of detectors and event reconstruction techniques recently developed at the ANU will be discussed.

EVIDENCE OF VARIATION OF THE ACCRETION FLOW GEOMETRY IN GRS 1915 + 105 FROM IXAE AND RXTE DATA

The Galactic microquasar GRS 1915 + 105 exhibits various types of light curves. There is, however, no understanding of when a certain type of light curve will be exhibited and only in a handful of cases, the transitions from one type to another have actually been observed. We study the detailed spectral properties in these cases to show that different classes have different ratio of the power-law photon and the blackbody photon. Since the power-law photons are from the Compton cloud, and the intensity of the power-law photon component depends on the degree of interception of the soft photons by the Compton cloud, we conclude that not only the accretion rate, but the accretion flow geometry must also change during a class transition.

Pulse profile stability of the Crab pulsar

We present an X-ray timing analysis of the Crab pulsar, PSR B0531+21, using archival RXTE data. We have investigated the stability of the Crab pulse profile, in soft (2–20 keV) and hard (30–100 keV) X-ray energies, over the last decade of RXTE operation. The analysis includes measurement of the separation between the two pulse peaks and the intensity and widths of the two peaks. We did not find any significant time dependency in the pulse shape. The two peaks have been stable in phase, intensity and width for the last ten years. The first pulse is relatively stronger at soft X-rays. The first pulse peak is narrower than the second peak in both soft and hard X-ray energies. Both the peaks show a slow rise and a steeper fall. The ratio of the pulsed photons in the two peaks is also constant in time.

External photon fields in Fermi bright blazars

The external Compton (EC) model is used to study the high energy emission of some blazars, in which the external photon field is considered to dominate inverse Compton radiation. We explore the properties of the external photon field through analyzing the FERMI LAT bright AGN sample within three months of the start of operations in sky-survey mode. In the sample, assuming the high energy radiation of low synchrotron peaked blazars is from the EC process, we find that the external photon parameter Uext/νext may not be a constant. Calculating synchrotron and inverse Compton luminosity from the quasi-simultaneous broadband spectral energy distributions, we find that they have an approximately linear relation. This indicates that the ratio of external photon and magnetic energy density is a constant in the comoving frame, implying that the Lorentz factor of the emitting blob depends on the external photon field and magnetic field. The result gives a strong constraint on the dynamic jet model.

Responses of the invasive Ricinus communis seedlings to competition and light

Ricinus is an invasive species. We assessed its responses to intra- and interspecific competition, and different intensities and spectral qualities of light. To evaluate resource portioning, we obtained biomass measurements of juveniles in different densities of co-specifics and another species; we also compared the proportion of juveniles to determine if there is recruitment limitation. We obtained the same information for juveniles growing in different photosynthetic photon flux densities (PPFD) and ratios of red to far-red wavelengths (R/FR). Competition and light did not limit recruitment, resulting in differences in biomass allocation only. Biomass decreased more for plants subjected to interspecific competition than to intraspecific competition, suggesting that Ricinus is both a poor intra- and interspecific competitor. Juveniles growing under reduced PPFD and R/FR differed in biomass allocation and morphology as do shade-intolerant species subjected to shading. Our results show that Ricinus presents high plasticity, which may contribute to its invasion ability.

Numerical simulation and modeling of spectral conversion by silicon nanocrystals with multiple exciton generation

Silicon nanocrystals (Si-NCs) were applied on the front surface of a conventional silicon solar cell. Considering absorption with multiple exciton generation (MEG) yields and consequently photoluminescence, the cell performance was simulated based on a numerical model founded on experimental results in literature. The results show that the cell efficiency could be prominently enhanced by MEG yields and spectral down-conversion. However, though MEG yields could reach 250% within Si-NCs, it only contributes 8.7% to the cell efficiency enhancement while wavelength shifting dominates the cell efficiency enhancement mechanism. Additionally, extraction factor which is defined as ratio of photons extracted from Si-NCs to the generated carries in Si-NCs is the most critical parameter for cell performance improvement. Therefore, to realize this novel structure cell, further experimental work should be lay on improving MEG efficiency as well as photoluminescence efficiency and optical confinement of the photoluminescence.

モリブデンターゲットＸ線管から放射されるＸ線スペクトルの推定計算式

A presumption calculating formula of the X-ray spectrum generated from a molybdenum target X-ray tube is presented. The calculation procedure is to add an amount of characteristic X-ray photons that corresponds to the ratio of characteristic photons and bremsstrahlung photons to the bremsstrahlung spectrum obtained using semiempirical calculation. The bremsstrahlung spectrum was calculated by using a corrected Tucker's formula. The corrected content was a formula for calculating the self-absorption length in the target that originated in the difference of the incident angle to the target of the electron and the mass stopping power data. The measured spectrum was separated into the bremsstrahlung component and the characteristic photon component, and the ratio of the characteristic photons and bremsstrahlung photons was obtained. The regression was derived from the function of the tube voltage. Based on this calculation procedure, computer software was constructed that can calculate an X-ray spectrum in arbitrary exposure conditions. The X-ray spectrum obtained from this presumption calculating formula and the measured X-ray spectrum corresponded well. This formula is very useful for analyzing various problems related to mammography by means of Monte Carlo simulations.

Testing the Copernican Principle with the kSZ Effect

The kinematic Sunyaev-Zel’dovich(kSZ) effect in a Lemitre-Tolman-Bondi(LTB) universe is discussed. We use the LTB universe model whose distance redshift relation coincides with the concordance ΛCDM model. The physical degrees of freedom on the last scattering surface(LSS) are fixed by using the Gamow’s criterion and other additional convenient conditions. We simulate the kSZ effect by solving null geodesic equations numerically. It seems to be difficult to explain observational results with adiabatic inhomogeneities on the LSS. This difficulty would be resolved by introducing the inhomogeneity of the matter to photon ratio on the LSS, which corresponds to the isocurvature perturbation.

Effect of the variation of the Higgs vacuum expectation value upon the deuterium binding energy and primordial abundances of D and4He

Aims. We calculate the constraints on the time variation of the Higgs vacuum expectation value from Big Bang Nucleosynthesis. Methods. Starting from the calculation of the deuterium binding-energy, as a function of the pion-mass and using the NN-Reid 93 potential, we calculate the abundances of primordial D and 4 He by modifying Kawano’s code. The Higgs vacuum expectation value (v) and the baryon to photon ratio (ηB) enter the calculation as free parameters. By using the observational data of D and 4 He, we set constraints on ηB and on the variation ofv, relative to a constant value of ΛQCD.

Measuring the fluorescent quantum efficiency of indocyanine green encapsulated innanocomposite particulates

We present results of a fluorescent quantum efficiency (ΦF) study on the encapsulation of the near-infrared dye indocyanine green(ICG) in bioresorbable calcium phosphate nanoparticles (CPNPs). TheΦF (described as the ratio of photons emitted to photons absorbed) provides aquantitative means of describing the fluorescence of an arbitrary molecule.However, standard quantum efficiency measurement techniques provide only theΦF of the smallest fluorescing unit—in the case of a nanoparticle suspension,the nanoparticle itself. This presents a problem in accurately describing theΦF of fluorophores embedded in an inorganic nanoparticle. Combining the incidenceof scattering with an evaluation of the differences in local electric field andphotochemical environment, we have developed a method to determine theΦF of the constituent fluorescent molecules embedded in such a nanoparticle, whichprovides a more meaningful comparison with the unencapsulated fluorophore. Whileapplicable to generic systems, we present results obtained by our method for theICG–CPNP in a phosphate buffered 0.15 M saline solution (PBS, pH 7.4)—specifically,ΦF, free dye = 0.027 ± 0.001,ΦF, particle = 0.053 ± 0.003, and for the individual encapsulated molecules,ΦF, molecule = 0.066 ± 0.004. The method developed also provides insight into the influences of encapsulation and keyparameters to engineer resonant enhancement effects from the emission of the encapsulatedfluorophores corresponding to an eigenmode of the embedding particle for tailored opticalproperties.

A Little Inflation in the Early Universe at the QCD Phase Transition

We explore a scenario that allows for a strong first order phase transition of QCD at a non-negligible baryon number in the early Universe and its possible observable consequences. The main assumption is a quasistable QCD-vacuum state that leads to a short period of inflation, consequently diluting the net baryon to photon ratio to today's observed value. A strong mechanism for baryogenesis is needed to start out with a baryon asymmetry of order unity, e.g., as provided by Affleck-Dine baryogenesis. The cosmological implications are direct effects on primordial density fluctuations up to dark matter mass scales of M{max}∼1-10M{⊙}, change in the spectral slope up to M{max}∼10{6}-10{8}M{⊙}, production of strong primordial magnetic fields and a gravitational wave spectrum with present day peak strain amplitude of up to h{c}(ν{peak})∼5×10{-15} around ν{peak}∼4×10{-8} Hz.

A BOUNDING ESTIMATE OF NEUTRON DOSE BASED ON MEASURED PHOTON DOSE AROUND SINGLE PASS REACTORS AT THE HANFORD SITE

Neutron and photon radiation survey records have been used to evaluate and develop a neutron to photon (NP) ratio to reconstruct neutron doses to workers around Hanford's single pass reactors that operated from 1945 to 1972. A total of 5,773 paired neutron and photon measurements extracted from 57 boxes of survey records were used in the development of the NP ratio. The development of the NP ratio enables the use of the recorded dose from an individual's photon dosimeter badge to be used to estimate the unmonitored neutron dose. The Pearson rank correlation between the neutron and photon measurements was 0.71. The NP ratio best fit a lognormal distribution with a geometric mean (GM) of 0.8, a geometric standard deviation (GSD) of 2.95, and the upper 95 th % of this distribution was 4.75. An estimate of the neutron dose based on this NP ratio is considered bounding due to evidence that up to 70% of the total photon exposure received by workers around the single pass reactors occurs during shutdown maintenance and refueling activities when there is no significant neutron exposure. Thus when this NP ratio is applied to the total measured photon dose from an individual film badge dosimeter, the resulting neutron dose is considered bounded.

Highly sensitive and selective label-free optical detection of mercuric ions using photon upconverting nanoparticles

We demonstrate a fluorescence-based, label-free detection scheme that reports the presence of Hg(II) ion using photon upconverting nanoparticles. A single-stranded DNA containing a number of thymine bases to be used as the Hg 2+-capturing element is covalently attached to the photon upconverting NaYF 4:Yb 3+,Tm 3+ nanoparticles. Under the illumination of 980 nm laser, energy transfer takes place between the NaYF 4:Yb 3+,Tm 3+ nanoparticles as the donor and SYBR Green I, a DNA intercalating dye, as the acceptor. By monitoring the ratio of the acceptor emission to the donor emission, we can quantitatively detect the presence of the mercuric ions with a directly observed detection limit of 0.06 nM. The remarkably high signal-to-noise ratio of photon upconverting particles leads to very high sensitivity and specificity without the need of fluorophore labeling. The sensor also does not suffer from photobleaching.

Anthropic explanation of the dark matter abundance

I use Bousso's causal diamond measure to make a statistical prediction for the dark matter abundance, assuming an axion with a large decay constant fa >> 1012 GeV. Using a crude approximation for observer formation, the prediction agrees well with observation: 30% of observers form in regions with less dark matter than we observe, while 70% of observers form in regions with more dark matter. Large values of the dark matter ratio are disfavored by an elementary effect: increasing the amount of dark matter while holding fixed the baryon to photon ratio decreases the number of baryons inside one horizon volume. Thus the prediction is rather insensitive to assumptions about observer formation in universes with much more dark matter than our own. The key assumption is that the number of observers per baryon is roughly independent of the dark matter ratio for ratios near the observed value.

SU-FF-T-579: Comparison of Helical Tomotherapy and Mixed Beam Treatment Plans for Superficial Parotid Cancers

Purpose: To compare helical tomotherapy (HT) with mixed beam therapy (electron and IMRT) plans for a superficial parotid treatment. Method and Materials: Mixed beam and HT dose plans were developed for a patient with a superficial parotid gland tumor. Seven mixed beam plans included a 7‐field photonIMRT plan optimized on top of a single en‐face, 16‐MeV electron beam dose distribution. The ratio of photon to electron beam weights (at depth R100) were 1:0 (IMRT only), 2:1, 1:1, 1:2, 1:3, 1:4, and 0:1 (electrons only). Planning objectives for HT plans were set as closely as possible to those in the mixed beam plans, and were determined using our clinical planning protocol for head and neck cancers. The resulting dose distribution from each plan was evaluated using multiple dose metrics for the planning target volume (PTV) and normal tissues.Results: Dose homogeneity, D95%‐5%, was best for HT (0.94 Gy), and worst for electrons (7.19 Gy), but improved with mixed beam (0.99 Gy for 1:3) to nearly equal that of HT. Conformity index was 0.69 for HT and 0.78 for IMRT, but improved with mixed beam (0.80 for 2:1). Mean dose to the contralateral parotid was 16.0 Gy for HT and 20.1 Gy for IMRT, but improved with mixed beam (9.8 Gy for 1:4). Similar normal tissue results were found for the spinal cord, eyes, lens, optic nerves, and contralateral eye. Conclusions: Utilizing IMRT in mixed beam therapy improves dose homogeneity while taking advantage of the finite electron range to spare nearby critical structures. In this case, mixed beam therapy plans were comparable with or superior to HT and IMRT for the PTV and normal tissues.Conflict of Interest: This work was supported in part by TomoTherapy, Inc.

A free-space-based differential phase shift quantum key distribution scheme with higher key creation efficiency

Differential phase shift quantum key distribution scheme has been improved by introducing a passive path selection structure at the transmitter including two polarization controllers used to mark the photon pulses and a polarizing beam splitter to distinguish these pulses so that can make different time delay at the receiver. Theoretical analysis indicates that a free-space-based differential phase shift quantum key distribution system with this proposed improvement will have high efficiency with the utilization ratio of photons reaching 100% under ideal condition.

Energy transfer in crystalline Er 3+,Yb 3+:Sc 2O 3

The use of Yb 3+ as a sensitizer for Er 3+ doped laser materials is a common technique because of the high Yb 3+ absorption cross sections. Energy transfer processes from Yb 3+ to Er 3+ in Sc 2O 3 are studied by two different methods. Transfer parameters describing the interactions between Er 3+ and Yb 3+ ions are obtained on the one hand from the ratio of emitted photons around 1.55 μm by Er 3+ ions and around 1 μm by Yb 3+ ions at cw excitation of Yb 3+, on the other hand by lifetime measurements of Yb 3+ ions in the codoped samples. Laser experiments are performed to study the suitability of Er 3+,Yb 3+:Sc 2O 3 as a laser material. Comparisons with energy transfer in Er 3+,Yb 3+:glass are made.

Spectral shape and photon fraction as signatures of the Greisen-Zatsepin-Kuzmin cutoff

With the prospect of measuring the fraction of arriving secondary photons, produced through photo-pion energy-loss interactions of ultra-high-energy cosmic ray (UHECR) protons with the microwave background during propagation, we investigate how information about the local UHECR source distribution can be inferred from the primary (proton) to secondary (photon) ratio. As an aid to achieve this, we develop an analytic description for both particle populations as a function of propagation time. Through a consideration of the shape of the Greisen-Zatsepin-Kuzmin cutoff and the corresponding photon fraction curve, we investigate the different results expected for both different maximum proton energies injected by the sources, as well as a change in the local source distribution following a perturbative deformation away from a homogeneous description. At the end of the paper, consideration is made as to how these results are modified through extragalactic magnetic field effects on the proton's propagation. The paper aims to demonstrate how the shape of the cosmic ray flux in the cutoff region, along with the photon fraction, are useful indicators of the cutoff origin as well as the local UHECR source distribution.

A fiber-based differential phase shift quantum key distribution scheme with higher key creation efficiency

In this paper, a differential phase shift key distribution system with a selectable delay unit is proposed, in which higher key creation efficiency can be achieved. A photon from a single-photon source is split into four pulses with the same time interval T through two cascaded Mach–Zehnder interferometers. In Bob’s site, a 4 T delay loop with an optical switch is employed to reuse the two end pulses discarded in the conventional differential phase shift scheme, and then entire superposition of the all single photon pulses is achieved. The utilization ratio of photons can reach 100% in perfect condition.

Growth and photosynthesis of Chinese cabbage plants grown under light-emitting diode-based light source

We compared growth and the content of sugar, protein, and photosynthetic pigments, as well as chlorophyll fluorescence parameters in 15- and 27-day-old Chinese cabbage (Brassica chinensis L.) plants grown under a high-pressure sodium (HPS) lamps or a light source built on the basis of red (650 nm) and blue (470 nm) light-emitting diodes (LEDs) with a red to blue photon ratio of 7: 1. One group of plants was grown at a photosynthetic photon flux (PPF) level of 391 ± 24 μ mol/(m2 s) (normal level); the other, at a PPF level of 107 ± 9 μ mol/(m2 s) (low light). Plants of the third group were firstly grown at the low light and then (on the 12th day) transferred to the normal level. When grown at the normal PPF level, the plants grown under LEDs didn’t differ from plants grown under HPS lamps in shoot fresh weight, but they showed a lower root fresh and dry weights and the lower content of total sugar and sugar reserves in the leaves. No differences in the pigment content and photosystem II quantum yield were found; however, a higher Chl a/b ratio in plants grown under LEDs indicates a different proportion of functional complexes in thylakoid membranes. The response to low light conditions was mostly the same in plants grown under HPS lamps and LEDs; however, LED plants showed a lower growth rate and a higher nonphotochemical fluorescence quenching. In the case of the altered PPF level during growth, the plant photosynthetic apparatus adapted to new conditions of illumination within three days. Plants grown under HPS lamps at a constant normal PPF level and those transferred to the normal PPF level on the 12th day, on the 27th day didn’t differ in shoot fresh weight, but in plants grown under LEDs, the differences were considerable. Our results show that LED-based light sources can be used for plant growing. At the same time, some specific properties of plant photosynthesis and growth under these conditions of illumination were found.