Geometrical Optics applied to 1D Site Response of Inhomogeneous Soil Deposits

The technique referred as Geometrical Optics entails considering the wave propagation in a heterogeneous medium as if it happened with infinitely small wavelength. This classic simplification allows to obtain useful approximate analytical results in cases where complete description of the waveform behavior is virtually unattainable, hence its wide use in Physics. This approximation is also commonly termed Ray Theory, and it has already been thoroughly applied in Seismology. This text presents an application of Geometrical Optics to 1D Site Response (1DSR): it is used herein to, first, explain and elucidate the generality of some previous observations and results; second, to partially settle an open question in 1DSR, namely “what are the equivalent homogeneous properties that yield the same response, in terms of natural frequencies and resonance amplitude, for a certain inhomogeneous site?”, provided few assumptions

Geometrical Optics applied to 1D Site Response of Inhomogeneous Soil Deposits

The technique referred as Geometrical Optics entails considering the wave propagation in a heterogeneous medium as if it happened with infinitely small wavelength. This classic simplification allows to obtain useful approximate analytical results in cases where complete description of the waveform behavior is virtually unattainable, hence its wide use in Physics. This approximation is also commonly termed Ray Theory, and it has already been thoroughly applied in Seismology. This text presents an application of Geometrical Optics to 1D Site Response (1DSR): it is used herein to, first, explain and elucidate the generality of some previous observations and results; second, to partially settle an open question in 1DSR, namely “what are the equivalent homogeneous properties that yield the same response, in terms of natural frequencies and resonance amplitude, for a certain inhomogeneous site?”, provided few assumptions

X-Ray Polarization of Solar Flares Measured with Rhessi

The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure it with different missions. The high energy range, in particular, has very rarely been explored, due to its greater instrumental difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study six X-class and 1 M-class flares in the energy range between 100 and 350 keV. Using RHESSI as a polarimeter requires the application of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements show polarization values between 2 and 54%, with errors ranging from 10 to 26% in 1σ level. In view of the large uncertainties in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme propertie

The effect of temperature and enzyme concentration in the transesterification process of synthetic microalgae oil

Throughout the world, the fossil fuel has supplied around the 80% of the energetic requirements, in Colombia alone 95.1% of energetic demand is made by the transportation sector solely, supplied by oil, kerosene, gasoline and diesel, this sector has an extremely small participation with biofuel of 3%, which is represented only by biodiesel. Microalgae had been proposed as biofactories with a remarkable third generation biofuels production. The culture of the microorganism comprehends interesting characteristics as countless environments where its natural growth could be replicated in fresh, salty and even sewage waters, with a higher growth rate and a higher oil production. The implementation of enzymes in the transesterification process have generated a good curiosity in the field, due to its mild reactions conditions, lesser energetic requirements, a high standard in the selection of the enzymes with the objective of avoiding the formation of soaps, creating in this way cleaner products and sub-products, in which the separation of the phases biodiesel/glycerol, give the possibility to recuperate the bio catalyzer and high output of reactions. However, the high volume of medium required to obtain lipids is one of the major drawbacks to test the viability of these enzymes. The present study aims to design an enzymatic transesterification process for the production of biodiesel form synthetic Chlorella oil. The synthetic oil was designed according to the lipid profile of C 16:0, C16:1, C18:0, C18:1, C18:2 and C18:3 from Chlorella spp CHL2 cultured on Bold Basal media under limited concentrations of NaNO3. The enzymatic transesterification efficiency was evaluated by the implementation of a 22 experimental factorial design (temperature and lipase concentration) under a 3: 1 molar ratio of alcohol:oil and a fixed reaction time of 6 hours. The obtained results show that, in order to obtain superior yields of biodiesel (>91%) the transesterification process must be carried out under temperature conditions close to 38°C and lipase concentrations of 5%

A method to localize gamma-ray bursts using POLAR

The hard X-ray polarimeter POLAR aims to measure the linear polarization of the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts (GRBs). The position in the sky of the detected GRBs is needed to determine their level of polarization. We present here a method by which, despite of the polarimeter incapability of taking images, GRBs can be roughly localized using POLAR alone. For this purpose scalers are attached to the output of the 25 multi-anode photomultipliers (MAPMs) that collect the light from the POLAR scintillator target. Each scaler measures how many GRB photons produce at least one energy deposition above 50 keV in the corresponding MAPM. Simulations show that the relative outputs of the 25 scalers depend on the GRB position. A database of very strong GRBs simulated at 10201 positions has been produced. When a GRB is detected, its location is calculated searching the minimum of the chi2 obtained in the comparison between the measured scaler pattern and the database. This GRB localization technique brings enough accuracy so that the error transmitted to the 100% modulation factor is kept below 10% for GRBs with fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will be useful for those cases where no other instruments are simultaneously observing the same field of view.Comment: 13 pages, 10 figure

The Zagros Epipalaeolithic revisited: New excavations and 14C dates from Palegawra cave in Iraqi Kurdistan

Palegawra cave, alongside its neighbouring Zarzi, has been an emblematic site of the Epipalaeolithic (Zarzian) cultural horizon in the NW Zagros of Southwest Asia ever since its first exploration in 1951 by Bruce Howe and Robert Braidwood in the context of the Iraq-Jarmo project. At the time scientific excavation, sampling and analysis methods were either underdeveloped or did not exist. In this paper we present the first results of new excavations at Palegawra conducted in 2016–2017 by the Eastern Fertile Crescent (EFEC) project, a research collaboration of the University of Liverpool and the Sulaymaniyah Directorate of Antiquities and Heritage. Our research has produced the first radiometric evidence pushing back the chronology of the NW Zagros Epipalaeolithic to the Last Glacial Maximum, thus fully aligning it with Epipalaeolithic facies until now known only from the Levant and the south Anatolian coast. We have also unearthed, for the first time in the Palaeolithic of the Zagros, direct archaeobotanical evidence for hitherto elusive Zarzian plant exploitation and the vegetation of the NW Zagros piedmont zone from the LGM to the end of the Lateglacial (~19,600–13,000 cal BP). The new Palegawra chronology alongside our detailed studies of its material culture and faunal and botanical assemblages suggest that the prevailing Epipalaeolithic habitation pattern in the NW Zagros (centred on generalised persistent occupations of small caves and rock-shelters alongside task-oriented ephemeral open-air campsites) remained an enduring characteristic of the Zarzian horizon throughout this period. The Palegawra data clearly show that neither resource levels and climate conditions nor geographic and/or cultural isolation provide adequate explanations for the stability and longevity of Zarzian lifeways during this long timespan. More fieldwork is required, including the discovery, excavation and intensive sampling of other Zarzian sites, for reaching a datainformed understanding of the nature and evolution of the NW Zagros Epipalaeolithic

The influence of albedo on the size of hard X-ray flare sources

Context: Hard X-rays from solar flares are an important diagnostic of particle acceleration and transport in the solar atmosphere. Any observed X-ray flux from on-disc sources is composed of direct emission plus Compton backscattered photons (albedo). This affects both the observed spectra and images as well as the physical quantities derived from them such as the spatial and spectral distributions of accelerated electrons or characteristics of the solar atmosphere. Aims: We propose a new indirect method to measure albedo and to infer the directivity of X-rays in imaging using RHESSI data. Methods: Visibility forward fitting is used to determine the size of a disc event observed by RHESSI as a function of energy. This is compared to the sizes of simulated sources from a Monte Carlo simulation code of photon transport in the chromosphere for different degrees of downward directivity and true source sizes to find limits on the true source size and the directivity. Results: The observed full width half maximum of the source varies in size between 7.4 arcsec and 9.1 arcsec with the maximum between 30 and 40 keV. Such behaviour is expected in the presence of albedo and is found in the simulations. A source size smaller than 6 arcsec is improbable for modest directivities and the true source size is likely to be around 7 arcsec for small directivities. Conclusions: While it is difficult to image the albedo patch directly, the effect of backscattered photons on the observed source size can be estimated. The increase in source size caused by albedo has to be accounted for when computing physical quantities that include the size as a parameter such as flare energetics. At the same time, the study of the albedo signature provides vital information about the directivity of X-rays and related electrons.Comment: 8 pages, 6 figures, A&A (accepted