bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Dating: Methodological Aspects
Authors: Smith B.W. , Aitken M.J. , Rhodes E.J. , Robinson P.D. , Geldard D.M.
Published: February 2017

We have utilised the 514 nm line from a 2 W argon ion laser in application to mineral grains of quartz, zircon and apatite, extracted from samples of archaeological relevance. In this dating technique the age-dependent population of trapped electrons is measured by optically stimulated luminescence (OSL) rather than by thermoluminescence (TL). Hence only light-sensitive traps are sampled. This is particularly advantageous for unburnt sediment because of the reliance for zero setting on exposure to sunlight prior to deposition. For OSL this is accomplished in a matter of minutes whereas for TL there is often a substantial residual, particularly in the case of quartz, even after twenty four hours or so. The difficulties which arise are discussed, and some promising results presented.
How Accurately do Thermoluminescence and Photoluminescence Dosimetry Systems Indicate the New ICRU Dose Quantities for Individual Monitoring?
Authors: Böhm J. , Piesch E. , Regulla D.F.
Published: February 2017

In 1985, the German-Swiss radiation protection association and the PTB organised an intercomparison programme for individual monitoring systems to find out whether these systems are able to measure the new dose equivalents H'(10) and H'(0.07) specified in ICRU Report 39. Twelve laboratories from Switzerland, Austria, England and the Federal Republic of Germany participated with 30 dosimetry systems including TLD systems for whole-body monitoring (13), TLD systems for extremity dosimetry (5), PLD systems (2), and film dosimetry systems (6). The dosemeters were irradiated with photons on the surface of an Alderson human phantom or an ICRU sphere. The range of the mean photon energy was 26 keV to 662 keV. It was observed that there are already some dosimetry systems of every type (TLD, PLD, etc) whose response, with respect to H'(10) and H'(0.07), does not vary appreciably with photon energy. However, in general, special effort is needed to implement the new dose quantities in routine monitoring.
Radiophotoluminescent Glass Reader
Authors: Barthe J.R. , Prigent R. , Chapuis J.C. , Chuiton R.
Published: February 2017

In spite of the fact that phosphate glasses have pre-dose levels higher than those of thermoluminescent materials, they are still used for certain specific applications in dosimetry and in particular for criticality dosimetry. Because of the non-availability of readers suitable for measurements of this type corresponding to doses ranging from a few tens of milligrays up to several grays, we designed and realised a laboratory reader. The reader resembles a conventional fluorimeter with optimised elements. Procedures such as the stabilisation of UV flux, limiting excitation times, temperature corrections, sequential reading etc. are ensured by an internal microprocessor. The resulting reader is compact. It has a high performance and level of reliability. A double readout procedure, before and after irradiation, enables doses to be estimated with a high degree of precision. Accuracy depends on the specific characteristics of the glass and in particular on its background noise.
LiF-TLD in the Microgray Dose Range Via Computerised Glow Curve Deconvolution and Background Smoothing
Authors: Horowitz Y.S. , Moscovitch M.
Published: February 2017

A computerised glow curve deconvolution technique (CGCD) and its application to the ultralow dose thermoluminescence (TL) glow curve of LiF:Mg,Ti (TLD-100) are described. The benefits in precision and minimum measurable dose (MMD) applied to TLD-100 are considerable. The CGCD analysis interpolatively estimates the background signal under peaks 4 and 5 which greatly reduces the errors introduced by inaccurate background subtraction due to second readout as well as eliminating the need for second readout. In addition, the error introduced via inaccurate separation of peak 3 is reduced and post-irradiation annealing is rendered unnecessary. An additional important feature of the CGCD method is the ability to reject/correct outliers in the glow curve. Assuming a MMD criterion of ±20% (1 SD) precision yields a MMD of 1.9 µGy (0.19 mrad) and 27 µGy (2.7 mrad) for CGCD and routine analysis respectively, i.e. an improvement in MMD of a factor 14.2.
Role of Alkaline Earth Sulphide Phosphors in Solid State Dosimetry
Authors: Rao R.P.
Published: February 2017

With the increasing use of nuclear energy, there is a need for a wider range of efficient dosemeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulphides (AES) have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono, binary and ternary sulphides of alkaline earths (IIa-VIb) have been prepared and their TL properties have been studied with respect to exposure (X ray) response and fading. In this paper, some results on MgS:Eu,Sm, (Ba, Ca)S:Cu and (Ba, Ca, Sr)S:Cu,Bi phosphors are presented. The possibilities of using these materials in practical solid state dosimetry are discussed.
The Control of Background in the Production of TL Dosemeters
Authors: Lucas A.C. , Kapsar B.M.
Published: February 2017

As ALARA becomes more and more real in personnel dosimetry, TL dosemeters have assumed the role of low level detectors. While, for earlier years, intrinsic backgrounds were considered a necessary part of the dosemeter, identification and control of background sources is presently an important part of TLD technology. Typical radioactive interferences have been identified for starting chemicals for calcium fluoride. Screening methods have been devised with quantitative limits which are related to dosemeter performance criteria. Residual strain and radiation exposure also produce both fixed backgrounds and background rates. The time and temperature dependence of the interferences have been reviewed and methods for minimising their magnitude devised.
Radiolyoluminescence Studies of Mannose
Authors: O'Hagan J.B. , Pearson A.J.
Published: February 2017

Radiolyoluminescence is the emission of light from an irradiated solid upon dissolution. Mannose is closely tissue-equivalent for both high and low LET radiations. Results are reported on the batch to batch variations in sensitivity and dose thresholds for mannose powder. Absorbed dose-response curves are presented. Methods of increasing sensitivity and lowering dose thresholds and the potential use of mannose for practical dosimetry are discussed.
Incorporation of Monte Carlo Electron Interface Studies into Photon General Cavity Theory
Authors: Horowitz Y.S. , Moscovitch M. , Mack J.M. , Hsu H. , Kearsley E.
Published: February 2017

Electron Monte Carlo calculations using CYLTRAN and a new PHSECE (photon produced secondary electrons) technique were carried out to estimate electron fluences and energy deposition profiles near LiF/Al and LiF/Pb material interfaces undergoing 60Co irradiation. Several interesting and new features emerge: (i) Although the build-up of the secondary electron fluences at the interfaces of the irradiated media is approximately exponential, the value of the electron mass fluence build-up coefficient, ?, is not equal to the electron mass fluence attenuation coefficient, ß. (ii) The ß value of the attenuation of the gamma generated electron fluences at the cavity-medium interfaces is strongly dependent on the Z of the adjacent material. (iii) For LiF/Pb there is a significant 'intrusion' energy deposition mode arising from 'side-scattering' in the wall (Pb) material. These new features of interface dosimetry (at least (i) and (ii)) are incorporated into photon general cavity theory and compared with experimental data.
Ion Dose Response of TSEE of SiC Films
Authors: Huzimura R. , Miyagawa S. , Miyagawa Y. , Shimazu K.
Published: February 2017

TSEE curves of CVD ß-SiC films were measured in a high vacuum system after 100 keV He+ or Ar+ bombardment in the dose range between 10-9 and 10-2 C.mm-2. The main peak around 150 oC increases sublinearly up to 10-4 C.mm-2 and then begins to decrease, while the broad peak centred around 200 oC continues to grow until 10-2 C.mm-2. Based on the Lindhard theory, the experimental dependence of the main peak intensity on the He+ incident energy is analysed to attribute the peak mainly to exoelectron sources produced by electron excitation. Further, an exponential relation between the main peak quenching and the broad peak increase is found and disturbances due to nuclear collisions are suggested as the origin of this effect. We conclude that the quenching of glow peaks of electronic origin and the growing of peaks due to disturbances can be used as a measure of collision energy deposited in solids.
TL and TSEE in Crystallised Li2B4O7:Cu Glass
Authors: Kutomi Y. , Tomita A. , Takeuchi N.
Published: February 2017

X ray irradiated crystallised Li2B4O7:Cu glass shows TL glow peaks at about (I) 90 oC, (II) 160 oC, (III) 200 oC, (IV) 260 oC and (V) 320 oC by heating at the rate of 20 oC.min-1. All the glow peaks show an emission spectrum peaked at 360 nm, which is due to 3d94s-3d10 transition in Cu+. By heating at 300 oC and cooling to RT followed by illumination with white light, peaks I, III and IV were repopulated, but peak II disappeared. TSEE from the X ray irradiated samples also showed peaks at temperatures corresponding to peaks I, II, III, IV and V, but peak II was missing. These facts suggest for peaks I, IV and V the reaction, Cu2+ + electron®Cu+*®Cu+ + h?, and for peak II Cuo + hole®Cu+*®Cu+ + h?.
Performance Tests of a CaSO4:Dy Based Thermoluminescence Personal Dosemeter
Authors: Azorin J. , Gutierrez A. , Niewiadomski T.
Published: February 2017

In order to replace LiF commercial thermoluminescence dosemeters (TLDs) now used in personnel monitoring, we developed a TLD personnel monitoring badge based on pellets of CaSO4:Dy bound in pure KBr placed in plastic holders provided with 0.8 mm Pb filters to compensate for the energy dependence of CaSO4:Dy. Performance tests, based on the proposals of international standards for TLDs intended to be used as general deep tissue personal dosemeters, were done by developing the detailed test methods both for the tests required by the International Atomic Energy Agency (fading, linearity, effect of fluorescent light and sunlight and stability under standard climatic condition) and to meet the requirements of the International Electrotechnical Commission (batch homogeneity, detection threshold, stability of zero point repeatibility and residual). Initial tests showed a high residual and an increase of inhomogeneity. However, these drawbacks were overcome by changing the annealing procedure and the readout conditions. Using these new conditions TLDs met all the requirements for personal dosemeters.
Results of a Comparative Study on Different Personnel Dosemeters
Authors: Pitt E. , Schalch D. , Scharmann A.
Published: February 2017

The response of thermoluminescence, radiophotoluminescence, thin-film exoelectron, pocket (pocket ion chamber) and film dosemeters were examined in gamma fields of different qualities, including mixed fields. The dosemeters were exposed to realistic radiation fields in nuclear plants. Nuclide spectra and radiation field quantities were determined by various measurements, e.g. by spectrometry, by dose rate measurements and by calculations. Thermoluminescence and exoelectron dosemeters provided by far the best results, particularly in the lower dose range. Throughout, the accordance of thermoluminescence and exoelectron dosemeter readings with respect to whole body exposure was better than ±20% between about 0.1 and 2 mSv. Larger discrepancies were observed in the presence of low energy ß radiation when using 7 to 15 mg.cm-2 detector window thicknesses.
Cross Sections for Production of Secondary Electrons by Charged Particles
Authors: Rudd (INVITED) M.E.
Published: February 2017

The availability of cross sections for the production of secondary electrons from ion or electron collisions is reviewed from the point of view of a potential user. Some recent measurements and empirical models are pointed out. New models are proposed which give differential and total cross sections for proton and electron impact.
A General Theory of DNA Strand Break Production by Direct and Indirect Effects
Authors: Chatterjee A. , Holley W.R.
Published: February 2017

A general theory of the production of strand breaks by energetic electrons and heavy charged particles has been developed. This theory is based on chemical and biochemical mechanisms and does not require adjustable parameters. In order to avoid the complexities of a cellular system, we have referenced our calculations to systems consisting of aqueous solutions of SV40 DNA containing different amounts of tris-HCl buffer. It appears from the calculations that at 500 mM tris, the strand break yields are similar to those observed in a cellular complex when normalised to account for DNA length. Furthermore, the results indicate that the indirect action is not negligible in creating strand breaks. The difference between DNA breaks with and without histones has also been analysed.
Comparison Between Indirect and Direct Effects for High and Low LET Radiations in SV40 DNA Strand Break Induction
Authors: Stanton J. , Taucher-Scholz G. , Schneider M. , Kraft G.
Published: February 2017

Using the OH radical scavengers Tris[hydroxymethyl] aminomethane (Tris) and ß-mercaptoethanol (MEth), we studied indirect and direct radiation effects of DNA in solution. SV40 DNA was exposed to low LET X rays and to heavy ion beams (11.4 MeV.u-120Ne, 12.5 MeV.u-1131Xe and 16 MeV.u-1238U) varying in LET. Cross sections for strand break induction were calculated from dose-effect curves in the presence and absence of protector. We found MEth was a more efficient OH radical scavenger than Tris. We also showed differences in the ability of each scavenger to protect against single and double strand breaks. The role of Tris radical formation as a possible explanation of these differences is discussed.
Spatial Distribution Patterns of Energy Deposition and Cellular Radiation Effects in Lung Tissue Following Simulated Exposure to Alpha Particles
Authors: Hofmann W. , Nösterer M. , Crawford-Brown D.J. , Hutticher A.
Published: February 2017

Randomly oriented sections of rat tissue have been digitised to provide the contours of tissue-air interfaces and the locations of individual cell nuclei in the alveolated region of the lung. Sources of alpha particles with varying irradiation geometrics and densities are simulated to compute the resulting random pattern of cellular irradiation, i.e. spatial coordinates, frequency, track length, and energy of traversals by the emitted alpha particles. Probabilities per unit track length, derived from experimental data on in vitro cellular inactivation and transformation, are then applied to the results of the alpha exposure simulations to yield an estimate of the number of both dead and viable transformed cells and their spatial distributions. If lung cancer risk is linearly related to the number of transformed cells, the carcinogenic risk for hot particles is always smaller than that for a uniform nuclide distribution of the same activity.
Calculations of Physical and Chemical Reactions with DNA in Aqueous Solution from Auger Cascades
Authors: Wright H.A. , Hamm R.N. , Turner J.E. , Howell R.W. , Rao D.V. , Sastry K.S.R.
Published: February 2017

Monte Carlo calculations are performed of the physical and chemical interactions in liquid water by electrons produced during Auger cascades resulting from the decay of various radionuclides. Estimates are also made of the number of direct physical and indirect chemical interactions that would be produced on DNA located near the decay site.
The Implications of Non-Linearity for Excitation Transfer in DNA
Authors: Baverstock K.F. , Cundall R.B.
Published: February 2017

Non-linear effects which arise from the coupling of anharmonic interactions can completely change excitation transport through molecular chains. The consequences of this for an understanding of the effect of ionising radiation on DNA are discussed. We consider that these effects should be taken into account in the interpretation of experimental data.
The Radiation Chemistry of Glycylglycine in Aqueous Solutions
Authors: Yoshida H. , Bolch W.E. , Turner J.E. , Jacobson K.B.
Published: February 2017

This research was initiated to test the validity of predictions based on Monte Carlo calculations of the effects of ionising radiation on a simple dipeptide in aqueous solutions. The yields of the major radiolytic products resulting from the interactions of free radicals produced in water with glycylglycine were quantitatively analysed for X irradiated solutions. As reported in a companion paper by Bolch et al at this Symposium, excellent agreement was obtained between the results of the experiments and the Monte Carlo calculations. In this paper, the product yields were compared with those reported in 1973 by Garrison et al, who used 60Co gamma rays at much higher dose rates than the X rays in this study. As expected, yields in the two experiments were somewhat different, reflecting the differences in LET and dose rate. The glycylglycine concentration effect, the stoichiometric relationships and contribution of the primary and the secondary radicals in the formation of products are discussed.
Measurements of the Distributions of Separations Between Paired Ions After Passing Through Mylar Foils
Authors: Marino S.A. , Harvey J.R. , Brenner D.J. , Rossi H.H.
Published: February 2017

Measurements of the distributions of interatomic separations for 3.7 MeV diatomic deuterons after passing through Mylar foils 6.4, 10.2 and 19.0 µm thick have been made. CR-39 etched track plastic was used to register the particle tracks. After etching, the resulting pits were photographed using a scanning electron microscope and measurements of the track separations were made at a depth of 5 to 6 µm in the CR-39, with a minimum resolvable separation of 200 to 300 nm. Comparisons made with separation distributions calculated using previous measurements of multiple scattering angular distributions and a simplified version of the scattering theory of Marion and Zimmerman show reasonable agreement, especially for the thicker Mylar.
Electron-Hole Traps and Thermoluminescence of the LaCl3:TR Single Crystals
Authors: Kuzakov S.M.
Published: February 2017

LaCl3:TR single crystals can be effectively used in thermoluminescence dosimetry of X and gamma radiation. By means of thermoluminescence and thermo-current methods (77 - 600 K) we have studied the electron and hole traps, thermoluminescence spectra and mechanisms of recombination in LaCl3-TRCl3 crystals after X irradiation or selective photo-excitation. In undoped LaCl3 we have found the hole centres with activation energy E = 0.13 eV (the peak TL at 111 K) which can be attributed to the self-trapped holes (Vk). The glow curves of LaCl3-TR crystals contain high temperature peaks at 460, 575 and 590 K. These peaks may be used as dosimetric ones and can be attributed to the electron excess impurity centres. In LaCl3 doped with TR3+ ions we have observed TL peaks at 117, 142 and 156 K which are associated with holes located in an environment of Pr, Dy and Sm ions respectively (VkA centres).
Photoluminescence Dosimetry: Progress and Present State of Art
Authors: Piesch E. , Burgkhardt B. , Vilgis (INVITED) M.
Published: February 2017

The considerable progress in the readout technique for photoluminescent glass dosemeters is examined with emphasis on the application potential for individual monitoring. Radiophotoluminescence dosimetry (PLD) systems using a narrow pulsed UV laser excitation of flat glass detectors and an automatic readout are now commercially available and show improved dosimetric properties, in particular an internal pre-dose suppression, a dose range of 0.03 mSv to 10 Sv, a photon energy range extended down to 15 keV, a simultaneous indication of different dose quantities such as exposure Hx and directional dose equivalent H'(10) and the possibility of an estimation of radiation quality and incidence. Recent progress in PLD is reviewed with respect to the pulsed UV laser excitation, the improvement of the dosimetric properties by using an optimised flat glass dosemeter and the automatic readout which allows large scale evaluation and the application of different modes of evaluation, in particular vertical and horizontal scanning of the glass. The modern Toshiba readout systems FGD-10 and FGD-20 for glass dosemeters, prototype tested at KfK, are expected to be reliable dosimetry systems for large scale application in personnel and environmental monitoring, showing dosimetric properties which are comparable if not superior to those of TLD systems.
Thermoluminescence of High Temperature Glow Peaks of LiF at Various Irradiation Temperatures
Authors: Kitis G. , Charalambous S.
Published: February 2017

The variation of TL response of the high temperature glow peaks of LiF:Mg,Ti has been studied as a function of irradiation temperature and dose. The irradiation temperature range was from 77 to 473 K and the dose range from 1 to 104 Gy. The results show that there is strong dependence of the thermoluminescence response on irradiation temperature and dose.
Sensitised TLD-700 for Neutron-Gamma Ray Dosimetry at Radiation Protection Dose Levels
Authors: Horowitz Y.S. , Shachar B.B.
Published: February 2017

Computerised glow curve deconvolution (CGCD) has been used to study the TL dose response and the relative intensity of the high temperature peaks in both sensitised and 'as received' LiF:Mg,Ti (TLD-700). The 60Co gamma induced dose response of peak 7 is supralinear down to the lowest dose measurable (~2.5 mGy) and the supralinearity is strongly dependent on photon energy. In the sensitised material (the sensitisation procedure included 1000 Gy 60Co irradiation followed by a 340 oC, 30 min anneal), although the gamma induced dose response of peak 7 is linear, an intense high temperature background limits the minimum measurable dose to 500 µGy and 100 µGy for gamma and neutron irradiation respectively. We conclude that the method of peak 7/peak 5 ratios in both non-sensitised and sensitised TLD-700 is not suitable for neutron-gamma ray dosimetry at personal radiation protection dose levels.
Characterisation of LiF:Cu,Mg,P (GR-200) for Personnel Thermoluminescence Dosimetry
Authors: Horowiz Y.S. , Horowitz A.
Published: February 2017

We report the results of our dosimetric characterisation of hot-pressed GR-200 LiF:Cu,Mg,P chips for personnel radiation protection. The TL sensitivity was studied as a function of the maximum temperature of glow curve readout and heating rate. In order to achieve acceptable re-usability we recommend a maximum temperature of 240 ± 2 oC or alternatively 235 ± 5 oC, although the latter choice will lead to a significantly higher residual signal. The TL sensitivity is not a function of glow curve heating rate. We have also studied the dependence of the residual TL signal (TMAX = 240 ± 2 oC) on a large number of experimental and radiation field parameters. Our main conclusion is that the ratio of the second and subsequent readouts to first readout is, to a good approximation, independent of all parameters except for TMAX and its duration, LET and possibly the time between readouts. The dependence on LET arises from the preferential population of the high temperature peak at 270 oC in alpha particle and neutron irradiation. The use of 'unannealed' LiF:Cu,Mg,P individually calibrated dosemeters is thus possible in personnel dosimetry applications if the prior irradiation history of the dosemeters is permanently recorded and the proper corrections (of the order of 10%) are applied. This represents a serious shortcoming of the currently available dosemeters for personnel dosimetry applications.
Infrared Thermoluminescence Signals of TLD-300 (CaF2:Tm) Detectors
Authors: Jacob M. , Meissner P. , Rassow J.
Published: February 2017

In these experiments a silicon semiconductor photodiode was used to measure the TL signal of TLD-300 (CaF2:Tm) detectors irradiated with 60Co gamma rays, 226Ra alpha particles and fast neutrons (CIRCE, Essen). The applied dose values varied from 0.12 Gy to 14.3 Gy for gamma rays and from about 50 to 300 Gy for alpha particles and for neutrons the value was 5.9 Gy. Because of the high infrared sensitivity of the photodiode a high IR TL signal could be detected in addition to the infrared emission of the planchet. The infrared TL signal with a peak intensity at a wavelength of about 800 nm exhibited the same dose dependences as the visible one, but the amplitude was much higher with respect to the visible signal. Measurements showed that the IR and the visible emission must be caused by the same trap type.
Measurement of Skin Dose with TSEE From BeO
Authors: Aoki M. , Okabe S. , Nishikawa M. , Nishikawa T.
Published: February 2017

A commercial ceramic BeO disc (Thermalox 995) and a ZnO thin film were used as TSEE specimens. The ß ray sensitive surface layer of a TSEE specimen acts as a very thin absorbed dosemeter. The absorbed dose of ß rays was measured using an extrapolation ionisation chamber. The experimental value of the conversion factor between the number of exoelectrons emitted from a Thermalox 995 TSEE specimen and the absorbed dose in the thin surface layer of the same specimen was about 84 pGy per exoelectron, and the value for a ZnO thin film was about 96 µGy per exoelectron. By covering a TSEE specimen with a tissue-equivalent material layer of 7 mg.cm-2 thickness, an easy measurement of the individual dose equivalent, superficial, Hs(0.07), is possible without any information on ß ray irradiation energy.
Comparative Study of Trapping Parameters of LiF (TLD-100) from Different Production Batches
Authors: Bos A.J.J. , Piters T.M. , de Vries W. , Hoogenboom J.E.
Published: February 2017

Computerised glow curve analysis has been used to determine the trapping parameters of the main peaks of the thermoluminescent (TL) material LiF(TLD-100). The TL material (solid state chips) originated from six different production batches with at least 19 chips per batch. The maxima of glow peaks 2 to 5 are found at the same temperature within very small limits. The activation energy and frequency factor of the main glow peak (peak 5) of TLD-100 originating from two batches differ significantly from those of the other four investigated batches. Nevertheless, the sensitivity of glow peak 5 is more or less the same for all batches. The trapping parameters of glow peaks 2 to 4 of TLD-100 vary little from batch to batch. The measured half-life of peak 2 differed strongly from batch to batch. For all investigated peaks no correlation has been found between glow peak sensitivity and trapping parameters. The results of this study suggest that both defect concentration and nature of the trapping centres vary from batch to batch. It would appear that as a consequence of selection by the manufacturer, the differences between the batches in terms of total light output are small.
Ant circadian activity associated with brood care type
Authors: Fujioka Haruna , Abe Masato S. , Fuchikawa Taro , Tsuji Kazuki , Shimada Masakazu , Okada Yasukazu
Published: February 2017

In group-living animals, social interactions influence various traits including circadian activity. Maternal care, in particular, can have a strong effect on the circadian activity of parents or nurses across taxa. In social insects, nest-mates are known to have diverse activity rhythms; however, what kind of social environment is crucial in shaping an individual's rhythm is largely unknown. Here, we show that the focal brood types being taken care of (i.e. egg, larva and pupa) have significant effects on individual activity/rest rhythm, using the monomorphic ant
Diacamma
(putative species
indicum
). When isolated from a colony, nurses exhibited a clear circadian rhythm. However, when paired with eggs or larvae, they exhibited around-the-clock activity with no apparent rhythm. In contrast, a clear activity rhythm emerged when nurses were paired with a pupa, requiring little care. Such brood-type-specific changes in circadian activity are considered to arise from the difference in caretaking demands. Our finding may contribute to the understanding of the organization of a colony in the context of behavioural variability under different microenvironments.
Unravelling the illusion of flicker fusion
Authors: Umeton Diana , Read Jenny C. A. , Rowe Candy
Published: February 2017

For over 150 years, researchers have investigated the anti-predator function of animal patterns. However, this work has mainly focused on when prey remain still, and has only recently started to incorporate motion into the study of defensive coloration. As motion breaks camouflage, a new challenge is to understand how prey avoid predators while moving around their environment, and if a moving prey can ever be camouflaged. We propose that there is a solution to this, in that a ‘flicker fusion effect’ can change the appearance of the prey in the eyes of their predators to reduce the chances of initial detection. This effect occurs when a high contrast pattern blurs at speed, changing the appearance of the prey, which may help them better match their background. Despite being widely discussed in the literature, the flicker fusion effect is poorly described, there is no clear theoretical framework for testing how it might reduce predation, and the terminology describing it is, at best, rather confusing. Our review addresses these three key issues to enable researchers to formulate precise predictions about when the flicker fusion effect occurs, and to test how it can reduce predation.
Mapping poverty using mobile phone and satellite data
Authors: Steele Jessica E. , Sundsøy Pål Roe , Pezzulo Carla , Alegana Victor A. , Bird Tomas J. , Blumenstock Joshua , Bjelland Johannes , Engø-Monsen Kenth , de Montjoye Yves-Alexandre , Iqbal Asif M. , Hadiuzzaman Khandakar N. , Lu Xin , Wetter Erik , Tatem Andrew J. , Bengtsson Linus
Published: February 2017

Poverty is one of the most important determinants of adverse health outcomes globally, a major cause of societal instability and one of the largest causes of lost human potential. Traditional approaches to measuring and targeting poverty rely heavily on census data, which in most low- and middle-income countries (LMICs) are unavailable or out-of-date. Alternate measures are needed to complement and update estimates between censuses. This study demonstrates how public and private data sources that are commonly available for LMICs can be used to provide novel insight into the spatial distribution of poverty. We evaluate the relative value of modelling three traditional poverty measures using aggregate data from mobile operators and widely available geospatial data. Taken together, models combining these data sources provide the best predictive power (highest
r
2
= 0.78) and lowest error, but generally models employing mobile data only yield comparable results, offering the potential to measure poverty more frequently and at finer granularity. Stratifying models into urban and rural areas highlights the advantage of using mobile data in urban areas and different data in different contexts. The findings indicate the possibility to estimate and continually monitor poverty rates at high spatial resolution in countries with limited capacity to support traditional methods of data collection.
Oscillatory wall shear stress is a dominant flow characteristic affecting lesion progression patterns and plaque vulnerability in patients with coronary artery disease
Authors: Timmins Lucas H. , Molony David S. , Eshtehardi Parham , McDaniel Michael C. , Oshinski John N. , Giddens Don P. , Samady Habib
Published: February 2017

Although experimental studies suggest that lowandoscillatory wall shear stress (WSS) promotes plaque transformation to a more vulnerable phenotype, this relationship has not been examined in human atherosclerosis progression. Thus, the aim of this investigation was to examine the association between oscillatory WSS, in combination with WSS magnitude, and coronary atherosclerosis progression. We hypothesized that regions of low and oscillatory WSS will demonstrate progression towards more vulnerable lesions, while regions exposed to low and non-oscillatory WSS will exhibit progression towards more stable lesions. Patients (n= 20) with non-flow-limiting coronary artery disease (CAD) underwent baseline and six-month follow-up angiography, Doppler velocity and radiofrequency intravascular ultrasound (VH-IVUS) acquisition. Computational fluid dynamics models were constructed to compute time-averaged WSS magnitude and oscillatory WSS. Changes in VH-IVUS-defined total plaque and constituent areas were quantified in focal regions (i.e. sectors;n= 14 235) and compared across haemodynamic categories. Compared with sectors exposed to low WSS magnitude, high WSS sectors demonstrated regression of total plaque area (p< 0.001) and fibrous tissue (p< 0.001), and similar progression of necrotic core. Sectors subjected to low and oscillatory WSS exhibited total plaque area regression, while low and non-oscillatory WSS sectors demonstrated total plaque progression (p< 0.001). Furthermore, compared with low and non-oscillatory WSS areas, sectors exposed to low and oscillatory WSS demonstratedregressionof fibrous (p< 0.001) and fibrofatty (p< 0.001) tissue and similarprogressionof necrotic core (p= 0.82) and dense calcium (p= 0.40). Herein, we demonstrate that, in patients with non-obstructive CAD, sectors subjected to low and oscillatory WSS demonstrated regression of total plaque, fibrous and fibrofatty tissue, and progression of necrotic core and dense calcium, which suggest a transformation to a more vulnerable phenotype.
On the role of micro-inertia in enriched continuum mechanics
Authors: Madeo Angela , Neff Patrizio , Aifantis Elias C. , Barbagallo Gabriele , d’Agostino Marco Valerio
Published: February 2017

In this paper, the role of gradient micro-inertia termsη¯∥ ∇u,t∥2and free micro-inertia termsη∥P,t∥2is investigated to unveil their respective effects on the dynamic behaviour of band-gap metamaterials. We show that the termη¯∥ ∇u,t∥2alone is only able to disclose relatively simplified dispersive behaviour. On the other hand, the termη∥P,t∥2alone describes the full complex behaviour of band-gap metamaterials. A suitable mixing of the two micro-inertia terms allows us to describe a new feature of the relaxed-micromorphic model, i.e. the description of a second band-gap occurring for higher frequencies. We also show that a split of the gradient micro-inertiaη¯∥ ∇u,t∥2, in the sense of Cartan–Lie decomposition of matrices, allows us to flatten separately the longitudinal and transverse optic branches, thus giving us the possibility of a second band-gap. Finally, we investigate the effect of the gradient inertiaη¯∥ ∇u,t∥2on more classical enriched models such as the Mindlin–Eringen and the internal variable ones. We find that the addition of such a gradient micro-inertia allows for the onset of one band-gap in the Mindlin–Eringen model and three band-gaps in the internal variable model. In this last case, however, non-local effects cannot be accounted for, which is a too drastic simplification for most metamaterials. We conclude that, even when adding gradient micro-inertia terms, the relaxed micromorphic model remains the best performing one, among the considered enriched models, for the description of non-local band-gap metamaterials.
Variability in individual assessment behaviour and its implications for collective decision-making
Authors: O'Shea-Wheller Thomas A. , Masuda Naoki , Sendova-Franks Ana B. , Franks Nigel R.
Published: February 2017

Self-organized systems of collective behaviour have been demonstrated in a number of group-living organisms. There is, however, less research relating to how variation in individual assessments may facilitate group decision-making. Here, we investigate this using the decentralized system of collective nest choice behaviour employed by the ant
Temnothorax albipennis,
combining experimental results with computational modelling. In experiments, isolated workers of this species were allowed to investigate new nest sites of differing quality, and it was found that for any given nest quality, there was wide variation among individuals in the durations that they spent within each nest site. Additionally, individual workers were consistent in spending more time in nest sites of higher quality, and less time in those of lower quality. Hence, the time spent in a new nest site must have included an assessment of nest quality. As nest site visit durations (henceforth termed assessment durations) are linked to recruitment, it is possible that the variability we observed may influence the collective decision-making process of colonies. Thus, we explored this further using a computational model of nest site selection, and found that heterogeneous nest assessments conferred a number of potential benefits. Furthermore, our experiments showed that nest quality assessments were flexible, being influenced by experience of prior options. Our findings help to elucidate the potential mechanisms underlying group behaviour, and highlight the importance of heterogeneity among individuals, rather than precise calibration, in shaping collective decision-making.
Generalized Leaky Integrate-And-Fire Models Classify Multiple Neuron Types
Authors: Teeter Corinne , Iyer Ramakrishnan , Menon Vilas , Gouwens Nathan , Feng David , Berg Jim , Cain Nicholas , Koch Christof , Mihalas Stefan
Published: February 2017

In the mammalian neocortex, there is a high diversity of neuronal types. To facilitate construction of system models with multiple cell types, we generate a database of point models associated with the Allen Cell Types Database. We construct a series of generalized integrate-and-fire (GLIF) models of increasing complexity aiming to reproduce the spiking behaviors of the recorded neurons. We test the performance of these GLIF models on data from 771 neurons from 14 transgenic lines, with increasing model performance for more complex models. To answer how complex a model needs to be to reproduce the number of electrophysiological cell types, we perform unsupervised clustering on the parameters extracted from these models. The number of clusters is smaller for individual model types, but when combining all GLIF parameters 18 clusters are obtained, while 11 clusters are obtained using 16 electrophysiological features. Therefore, these low dimensional models have the capacity to characterize the diversity of cell types without the need for a priori defined features.
Crystal structure prediction by ionic network analysis: the example of (p–T–X)-structure relationships in olivines
Authors: Thomas Noel W.
Published: February 2017

The method of Ionic Network Analysis (INA) is defined by reference to the known crystal structures of olivine minerals. It is based on a reversible transformation between two alternative representations of ionic crystal structures: (a) the crystallographic and (b) the interactional. Whereas the former encompasses unit-cell parameters and atomic coordinates, the latter consists of selected interaction vectors between ions. Since the lengths and orientations of these vary only slightly between crystal structures obtained under systematically varying (p, T, X) conditions, they may be used to predict the crystal structures at intermediate (p, T, X) values by interpolation. Two interactional networks are constructed, one for the anions and the other for cations. As both networks lead to independent calculated values of the unit-cell parameters, it is possible to exploit the known, continuous (p, T, X) variations of cell parameters as normative constraints for the prediction of atomic coordinates within a predictive structural refinement procedure. Continuously varying structurally based parameters such as the volumes of cation coordination polyhedra may likewise be used. The choice of olivines for developing the method has been guided by the availability of pressure, temperature and compositional structural data for them. However, the ideas are expounded sufficiently generally for the method to be applied to other minerals.
Structures and thermal stability of the α-LiNH4SO4 polytypes doped with Er3+ and Yb3+
Authors: Sabalisck N. P. , Guzmán-Afonso C. , González-Silgo C. , Torres M. E. , Pasán J. , del-Castillo J. , Ramos-Hernández D. , Hernández-Suárez A. , Mestres L.
Published: February 2017

In order to clarify the polymorphism in the lithium sulfate family, LiRE
x
(NH4)1 − x
SO4 (0.5 ≤ x ≤ 4.0 mol%, nominal value; RE = Er3+, Yb3+ and Dy3+) crystals were grown from aqueous solution by slow evaporation between 298 and 313 K. The doping of the samples allowed us to obtain two polymorphic forms, α and β, of LiNH4SO4 (LAS). By means of X-ray diffraction (XRD) in single crystals, we determined the crystal structures of two new α-polytypes, which we have named α1- and α2-LAS. They present the same space group P21/c and the following relation among their lattice parameters: a
2 = −c
1, b
2 = −b
1, c
2 = −2a
1 − c
1. In order to evaluate the stability of the new α-polytypes, we performed thermal analysis, X-ray diffraction and dielectric spectroscopy on single crystals and polycrystalline samples over the cyclic temperature range: 190 → 575  → 190 K. The results obtained by all the techniques used in this study demonstrate that α-polytypes are stable across a wide range of temperatures and they show an irreversible phase transition to the paraelectric β-phase above 500 K. In addition, a comparative study of α- and β-polytypes shows that both polymorphic structures have a common axis, with a possible intergrowth that facilitates their coexistence and promotes the reconstructive α → β transition. This intergrowth was related to small anomalies detected between 240 and 260 K, in crystals with an α-habit.
Getting the chemistry right: protonation, tautomers and the importance of H atoms in biological chemistry
Authors: Bax Ben , Chung Chun-wa , Edge Colin
Published: February 2017

There are more H atoms than any other type of atom in an X-ray crystal structure of a protein–ligand complex, but as H atoms only have one electron they diffract X-rays weakly and are `hard to see'. The positions of many H atoms can be inferred by our chemical knowledge, and such H atoms can be added with confidence in `riding positions'. For some chemical groups, however, there is more ambiguity over the possible hydrogen placements, for example hydroxyls and groups that can exist in multiple protonation states or tautomeric forms. This ambiguity is far from rare, since about 25% of drugs have more than one tautomeric form. This paper focuses on the most common, `prototropic', tautomers, which are isomers that readily interconvert by the exchange of an H atom accompanied by the switch of a single and an adjacent double bond. Hydrogen-exchange rates and different protonation states of compounds (e.g. buffers) are also briefly discussed. The difference in heavy (non-H) atom positions between two tautomers can be small, and careful refinement of all possible tautomers may single out the likely bound ligand tautomer. Experimental methods to determine H-atom positions, such as neutron crystallography, are often technically challenging. Therefore, chemical knowledge and computational approaches are frequently used in conjugation with experimental data to deduce the bound tautomer state. Proton movement is a key feature of many enzymatic reactions, so understanding the orchestration of hydrogen/proton motion is of critical importance to biological chemistry. For example, structural studies have suggested that, just as a chemist may use heat, some enzymes use directional movement to protonate specific O atoms on phosphates to catalyse phosphotransferase reactions. To inhibit `wriggly' enzymes that use movement to effect catalysis, it may be advantageous to have inhibitors that can maintain favourable contacts by adopting different tautomers as the enzyme `wriggles'.
Land registration and landownership security
Authors: Abdulai Raymond Talinbe , Ochieng Edward
Published: February 2017

Purpose

The assertion that land registration guarantees landownership security is common knowledge. Thus, efforts at securing landownership in particularly, the developing world have concentrated on the formulation and implementation of land registration policies. However, over the years, whilst some studies claim that land registration assures security, a lot of other studies have established that security cannot be guaranteed by land registration. Also, there is evidence from research that has shown that land registration can be a source of ownership insecurity in some cases. The purpose of this paper is to critically analyse the underpinning principles of land registration and their application in order to establish whether or not land registration can actually guarantee ownership security.

Design/methodology/approach

It is a literature review paper that looks at the existing literature on landownership, security and land registration systems. The land registration principles that have been subjected to critical analysis are the publicity function of land registration, the legality of ownership emanating from land registration and the warranty provided by the State in land registration, specifically, under the Torrens system.

Findings

An analysis of the underpinning principles of land registration shows that land registration per se cannot guarantee ownership security and this helps to explain the findings of the numerous studies, which have established that landownership security cannot be assured by land registration. The paper concludes by identifying the right role of land registration as well as a mechanism that can effectively protect or secure landownership.

Practical implications

Land registration policies and programmes in the developing world are often funded by the international donor community and the findings provide useful insights regarding the actual role of land registration and for policy change in terms of what can secure landownership.

Originality/value

Even though there are two schools of thought regarding research on the link between land registration on one hand, and landownership security on the other, none of the studies has made an attempt to consider the nexus by critically examining the principles that underpin land registration to support their arguments.