Space-frequency model of amplified spontaneous emission and super-radiance in free electron laser operating in the linear and non-linear regimes

A three-dimensional, space-frequency model for the excitation of electromagnetic radiation in a free-electron laser is presented. The approach is applied in a numerical particle code WB3D, simulating the interaction of a free-electron laser operating in the linear and non-linear regimes. Solution of the electromagnetic excitation equations in the frequency domain inherently takes into account dispersive effects arising from the cavity and the gain medium. Moreover, it facilitates the consideration of statistical features of the electron beam and the excited radiation, necessary for the study of spontaneous emission, synchrotron amplified spontaneous emission (SASE), super-radiance and noise. We employ the code to study the statistical and spectral characteristics of the radiation generated in a pulsed beam free-electron laser operating in the millimeter wavelengths. The evolution of radiation spectrum, excited when a Gaussian shaped bunch with a random distribution of electrons is passing through the wiggler, was investigated.Comment: 9 page

Word-Slam Stories as Venues for Stimulating Learning and Developing Agency with Urban High School Students

Word-slam was used with our high school urban students as instrument and method to elicit engagement with learning and develop agency through personal storytelling. The word-slam text (as it appears on YouTube and in hard-copy format as well) was chosen due to its being a personal story and an alternative, artistic and critical form of text that our students could relate to directly as the format and content were relevant to their lives and experiences. By using the text as a mentor text and studying the author’s craft together, students were able to write, rewrite and develop their own word-slam stories, carving out a space for themselves to be seen and heard

New insights into the Upper Palaeolithic of the Caucasus through the study of personal ornaments. Teeth and bones pendants from Satsurblia and Dzudzuana caves (Imereti, Georgia)

The region of western Georgia (Imereti) in the Southern Caucasus has been a major geographic corridor for human migrations during the Middle and Upper Paleolithic. Data of recent research and excavations in this region display its importance as a possible route for the dispersal of anatomically modern humans (AMH) into northern Eurasia. Nevertheless, within the local research context, bone-working and personal ornaments have yet contributed but little to the Upper Palaeolithic (UP) regional sequence’s characterization. Here we present an archaeozoological, technological and use-wear study of pendants from two local UP assemblages, originating in the Dzudzuana Cave and Satsurblia Cave. The ornaments were made mostly of perforated teeth, though some specimens were made on bone. Both the manufacturing marks made during preparation and use-wear traces indicate that they were personal ornaments, used as pendants or attached to garments. Detailed comparison between ornament assemblages from northern and southern Caucasus reveal that they are quite similar, supporting the observation of cultural bonds between the two regions, demonstrated previously through lithic techno-typological affinities. Furthermore, our study highlights the importance attributed to red deer (Cervus elaphus) by the UP societies of the Caucasus in sharing aesthetic values and/or a symbolic sphere

Upper Palaeolithic genomes reveal deep roots of modern Eurasians.

We extend the scope of European palaeogenomics by sequencing the genomes of Late Upper Palaeolithic (13,300 years old, 1.4-fold coverage) and Mesolithic (9,700 years old, 15.4-fold) males from western Georgia in the Caucasus and a Late Upper Palaeolithic (13,700 years old, 9.5-fold) male from Switzerland. While we detect Late Palaeolithic-Mesolithic genomic continuity in both regions, we find that Caucasus hunter-gatherers (CHG) belong to a distinct ancient clade that split from western hunter-gatherers ∼45 kya, shortly after the expansion of anatomically modern humans into Europe and from the ancestors of Neolithic farmers ∼25 kya, around the Last Glacial Maximum. CHG genomes significantly contributed to the Yamnaya steppe herders who migrated into Europe ∼3,000 BC, supporting a formative Caucasus influence on this important Early Bronze age culture. CHG left their imprint on modern populations from the Caucasus and also central and south Asia possibly marking the arrival of Indo-Aryan languages.This research was supported by the European Research Council (ERC) Starting Grant to R.P. (ERC-2010-StG 263441). D.B., M.H and AM. were also supported by the ERC (295729-CodeX, 310763-GeneFlow and 647787-LocalAdaptation respectively). The National Geographic Global Exploration Fund funded fieldwork in Satsurblia Cave l from April 2013 to February 2014 (grant- GEFNE78–13). V.S. was supported by a scholarship from the Gates Cambridge Trust and M.G.L. by a BBSRC DTP studentship. C.G. was supported by the Irish Research Council for Humanities and Social Sciences (IRCHSS) ERC Support Programme and the Marie-Curie Intra-European Fellowships (FP7-IEF-328024). R.M. was funded by the BEAN project of the Marie Curie ITN (289966) and L.C. by the Irish Research Council (GOIPG/2013/1219). R.L.M. was funded by the ALS Association of America (2284) and Fondation Thierry Latran (ALSIBD). M.C. was supported by Swiss NSF grant 31003A_156853. We acknowledge Shota Rusataveli Georgian National Science Foundation as well as the DJEI/DES/SFI/HEA Irish Centre for High-End Computing (ICHEC) for the provision of computational facilities and Science Foundation Ireland (12/ERC/B2227) for provision of sequencing facilities. We thank Valeria Mattiangeli and Matthew D. Teasdale for their assistance.This is the final version of the article. It was first available from NPG via http://dx.doi.org/10.1038/ncomms991

Neandertal-Modern Human Contact in Western Eurasia: Issues of Dating, Taxonomy, and Cultural Associations

Supporting Assimilation views of Neandertal/modern human interaction, chronostratigraphic reasoning indicates that the “transitional” industries of Europe predate modern human immigration, in agreement with their association with Neandertals in the Châtelperronian at the Grotte du Renne and St.-Césaire. Supporting the Neandertals' species separateness and less developed cognition, those industries are alternatively claimed to relate to pioneer groups of modern humans; the latter would have been the true makers of the precocious instances of symbolic material culture that, under Assimilation, are assigned to the Neandertals. However, the taxonomy of the Kent's Cavern and Grotta del Cavallo dental remains is uncertain, and their poor stratigraphic context precludes dating by association. The opposite happens at the Grotte du Renne, whose stratigraphic integrity is corroborated by both taphonomy and dating. Not questioning that the Early Ahmarian is a cultural proxy for modern humans and a source for the Protoaurignacian of Europe, its claimed emergence ~46–49 ka ago at Kebara refl ects the dating of Middle Paleolithic charcoal—to be expected, because the Early Ahmarian units at the back of the cave are made up of reworked Middle Paleolithic sediments derived from the entrance. The dating of inherited material also explains the old results for the Aurignacian of Willendorf II and Geissenklösterle. At the latter, the dates on anthropically modified samples of the hunted taxa (reindeer and horse) place its Aurignacian occupations in the same time range as elsewhere in Europe, after ~40 ka ago. The hypothesis that Neandertal/modern human contact in Europe resulted in a process of assimilation in connection with the spread of the Protoaurignacian ~41.5 ka ago remains unfalsified.info:eu-repo/semantics/publishedVersio

Atmospheric and Fog Effects on Ultra-Wide Band Radar Operating at Extremely High Frequencies

The wide band at extremely high frequencies (EHF) above 30 GHz is applicable for high resolution directive radars, resolving the lack of free frequency bands within the lower part of the electromagnetic spectrum. Utilization of ultra-wideband signals in this EHF band is of interest, since it covers a relatively large spectrum, which is free of users, resulting in better resolution in both the longitudinal and transverse dimensions. Noting that frequencies in the millimeter band are subjected to high atmospheric attenuation and dispersion effects, a study of the degradation in the accuracy and resolution is presented. The fact that solid-state millimeter and sub-millimeter radiation sources are producing low power, the method of continuous-wave wideband frequency modulation becomes the natural technique for remote sensing and detection. Millimeter wave radars are used as complementary sensors for the detection of small radar cross-section objects under bad weather conditions, when small objects cannot be seen by optical cameras and infrared detectors. Theoretical analysis for the propagation of a wide “chirped” Frequency-Modulated Continuous-Wave (FMCW) radar signal in a dielectric medium is presented. It is shown that the frequency-dependent (complex) refractivity of the atmospheric medium causes distortions in the phase of the reflected signal, introducing noticeable errors in the longitudinal distance estimations, and at some frequencies may also degrade the resolution

A Systematic Approach for Calculating the Symbol Error Rate for the Entire Range of above and below the Threshold Point for the CE-OFDM System

Recently, the performance of the constant envelope OFDM (CE-OFDM) was analyzed in additive white Gaussian noise (AWGN) with the help of a closed-form approximated expression for the symbol error rate (SER). This expression was obtained with the assumption of having a high carrier-to-noise ratio (CNR) which, in effect, linearized the phase demodulator (the phase demodulator was implemented with an arctangent calculator) and simplified the analysis. Thus, this expression is not accurate for the lower range of CNR. As a matter of fact, it was already observed that there is a threshold point from which the simulated SER result vanishes from the theoretically obtained expression. In this paper, we present a systematic approach for calculating the SER without assuming having the high CNR case or using linearization techniques. In other words, we derive the SER for the nonlinear case. As a byproduct, we obtain a new closed-form approximated expression for the SER based on the Laplace integral method and the Edgeworth expansion. Simulation results indicate that the simulated results and those obtained from the new derived expression are very close for the entire range of bit energy-to-noise density ratio () above and below the threshold point

Quasi Optical Multi-Ray Model For Wireless Communication Link in Millimeter Wavelengths

The spectrum of millimeter waves lay above 30GHz. The band between 30GHz up to 300GHz is called Extremely High Frequencies (EHF). This wide spectrum is relatively free of users and have recently became relevant for realizations of wireless communications an radars, including the fifth generation (5G) of cellular communications. Due to the short wavelengths, the propagation of millimeter waves can be analyzed using quasi-optical ray techniques. We present a multi-ray analysis of millimeter wave wireless link in the presence of multipath. The analysis is applicable for indoor and outdoor links and considers reflections from walls and buildings. It is shown that line-of-sight is not necessarily required in scenarios where multiple reflections exist as in long corridors, canyons and tunnels. The theoretical results are verified experimentally with a link in the W-band (94GHz)