Rigorous derivation of coherent resonant tunneling time and velocity in finite periodic systems

The velocity $v_{res}$ of resonant tunneling electrons in finite periodic structures is analytically calculated in two ways. The first method is based on the fact that a transmission of unity leads to a coincidence of all still competing tunneling time definitions. Thus, having an indisputable resonant tunneling time $\tau_{res},$ we apply the natural definition $v_{res}=L/\tau_{res}$ to calculate the velocity. For the second method we combine Bloch's theorem with the transfer matrix approach to decompose the wave function into two Bloch waves. Then the expectation value of the velocity is calculated. Both different approaches lead to the same result, showing their physical equivalence. The obtained resonant tunneling velocity $v_{res}$ is smaller or equal to the group velocity times the magnitude of the complex transmission amplitude of the unit cell. Only at energies where the unit cell of the periodic structure has a transmission of unity $v_{res}$ equals the group velocity. Numerical calculations for a GaAs/AlGaAs superlattice are performed. For typical parameters the resonant velocity is below one third of the group velocity.Comment: 12 pages, 3 figures, LaTe

Additive Manufacturing of Heat Exchangers

The Advanced Research Project Agency (ARPA) includes the Advanced Research In Dry cooling (ARID) program. The objective of the ARID program is to develop technologies that allow power plants to achieve high thermal-to-electric energy conversion efficiency with zero net water consumption. The most direct method of achieving this goal is to improve the thermal efficiency of dry-cooled condensers by reducing the air-side thermal resistance without significantly increasing either the capital cost or the fan power required to operate these devices. One approach to this is the application of additive manufacturing to dry cooled condensers in order to obtain a low cost, high performance heat rejection system. Conversations with air-cooled heat exchanger manufacturers have resulted in aggressive cost targets that must be met in order to make this technology commercially viable in relevant first markets. A leading manufacturer of air-to-water heat exchangers has indicated that their “gold-standard” heat exchanger for HVAC&R applications achieves economic and thermal performance of approximately $10/kW­th and 7kWth/kg, respectively. This represents the limit of state-of-the-art air-cooled system performance that is the product of a many decades of engineering research; the limits of this technology are unlikely to change using conventional approaches since geometric constraints and costs are largely dictated by the manufacturing technology. The application of additive manufacturing to heat exchangers allows an unparalleled freedom in design. Fused Filament Fabrication (FFF) is a relatively low cost additive manufacturing process that involves depositing thermoplastic material layer by layer. The coupling of FFF with numerical models of air-side thermal fluid behavior has led to a novel, compact, high performance heat exchanger design that has been manufactured and validated experimentally. The heat exchanger features water and air in cross flow with an airfoil fin array on the air-side. Design paths towards cost and performance targets that will allow this technology to be competitive with industry targets have been identified and include: better understanding for manufacturing process constraints, filled material development, and air-side convection improvements. In the FFF process, physical geometrical constraints such as extrusion nozzle diameter and layer height have implications on thermal performance, overall resistance to heat transfer, and manufacturability. Typical thermoplastic thermal conductivities are 100 to 1000 times smaller than that of the aluminum and copper used in industry standard heat exchangers. Efforts to manufacture polymers that are filled with conductive materials such as carbon fiber, aluminum flakes, and graphite aim to decrease this gap by an order of magnitude. To be competitive with traditional air-cooled heat exchangers with material that is much less conductive, air-side convection optimization using Computational Fluid Dynamics (CFD) has been utilized to implement and validate advanced air-side geometries. An FFF manufactured heat exchanger that is cost and performance competitive with traditionally manufactured heat exchangers will open the door to a future in air-cooled systems that currently does not exist. This technology will allow heat exchangers to become lighter and fit in a smaller envelope as well as result in rapid replacement, high customization, fouling resistance and other secondary advantages

Piecing together the Lateglacial advance phases of the Reussgletscher (central Swiss Alps)

Exposure dating has substantially improved our knowledge about glacier advances during the Younger Dryas (YD) and the early Holocene. The glacier development after the Last Glacial Maximum (LGM) and the timing of morphologically evidenced, earlier Lateglacial re-advances is, however, still widely unknown. In this study we used 10Be surface exposure and radiocarbon dating to address these phases and corresponding landforms in the catchment of the former Reussgletscher (central Swiss Alps). We obtained clear indication for moraine deposition prior to the YD. The oldest samples predate the Bølling–Allerød interstadial (&gt;14.6&thinsp;ka). Morphostratigraphically even older lateral moraines, probably corresponding to terminal positions in the Lake Lucerne, could not be dated conclusively. Due to the geomorphological constraints of the sampling environment, the establishment of a local pre-YD chronology remains a challenge: moraines with adequate numbers of datable boulders were rarely preserved, and age attributions based on few samples are complicated by outliers.</p

Multiproxy evidence for environmental stability in the lesser caucasus during the late pleistocene

The Lesser Caucasus, situated between Asia and Europe, has long been recognised as a key region for the study of human evolution in terms of the timing and routes of dispersal, as well as, ecological adaptations. In particular, scholars have argued whether stable environments persisted in the region throughout the last glaciation, serving as a refugium for temperate biota, likely attracting human settlement and use. Here, we present the results of a multidisciplinary study of Karin Tak Cave, which contains sediments that accumulated between 48,000 and 24,000 cal yr BP. We examined biostratigraphic changes at the site by looking at the composition of fauna, which we hypothesise to be naturally accumulated, in different stratigraphic phases using traditional zooarchaeological approaches combined with collagen fingerprinting (ZooMS, Zooarchaeology by Mass Spectrometry). To gain further insights into regional palaeoenvironmental conditions, we also applied stable carbon and oxygen isotope analyses to faunal tooth enamel. The obtained results suggest that the onset of the last glaciation did not cause dramatic changes in regional environments, indicating that the Lesser Caucasus was a climatically and ecologically stable region despite significant global climatic changes during this period.1. Introduction 2. Study site 3. Materials and methods 3.1. Excavations 3.2. Dating 3.3. Morphology and taphonomy of faunal material 3.4. Zooarchaeology by mass spectrometry (ZooMS) 3.5. Stable isotope analyses 4. Results and interpretations 4.1. Chronology 4.2. Taphonomy 4.3. Morphological taxonomic identification 4.4. ZooMS identification 4.5. Stable isotope analyses 5. Discussion 5.1. Fossil accumulation and faunal spectrum 5.2. The Karin Taks fauna in a regional context 5.3. Palaeoenvironmental reconstructions 6. Conclusio

A biomolecular perspective on mobile pastoralism and its role in wider socioeconomic connections in the Chalcolithic South Caucasus

Mobile pastoralism is widely evoked when discussing technological developments, resource procurement, trans-regional interactions, and exchange networks in the South Caucasus. In this study, we conduct a comprehensive multiproxy investigation of faunal and botanical remains from the Middle to Late Chalcolithic in southern Armenia, at the high altitude Yeghegis-1 site, to directly assess herd mobility and human subsistence practices. Our findings indicate that, alongside intensified interregional connectivity, the inhabitants practised a rather sedentary form of multi-resource pastoralism, while maintaining herds at the site year-round. These results complement and expand upon models of pastoral mobility and its perceived crucial role in sustaining inter- and intra-regional connectivity. We argue that alternative models of increased intra-regional connectivity, focused on exchange between different specialised settled economies, need to be considered and further research is essential to unravel the complex interplay between subsistence, trade, and socio-economic dynamics.Introduction Results Site and Chronology Macrobotanical remains Morphology and taphonomy of faunal material Zooarchaeology by Mass Spectrometry Collagen stable isotope analysis of herd animals Bulk tooth enamel stable isotope analysis of herd animals Sequential tooth enamel stable isotope analysis of herd animals Discussion Subsistence ecology Herd mobility Herd management Reassessing pastoral mobility Resource Availability Limitations of Stud

Hunter-gatherer sea voyages extended to remotest Mediterranean islands

The Maltese archipelago is a small island chain that is among the most remote in the Mediterranean. Humans were not thought to have reached and inhabited such small and isolated islands until the regional shift to Neolithic lifeways, around 7.5 thousand years ago (ka)1. In the standard view, the limited resources and ecological vulnerabilities of small islands, coupled with the technological challenges of long-distance seafaring, meant that hunter-gatherers were either unable or unwilling to make these journeys2–4. Here we describe chronological, archaeological, faunal and botanical data that support the presence of Holocene hunter-gatherers on the Maltese islands. At this time, Malta’s geographical configuration and sea levels approximated those of the present day, necessitating seafaring distances of around 100 km from Sicily, the closest landmass. Occupations began at around 8.5 ka and are likely to have lasted until around 7.5 ka. These hunter-gatherers exploited land animals, but were also able to take advantage of marine resources and avifauna, helping to sustain these groups on a small island. Our discoveries document the longest yet-known hunter-gatherer sea crossings in the Mediterranean, raising the possibility of unknown, precocious connections across the wider region.Chronology Stone tools Faunal remains Environmental reconstruction Discussio

Preliminary paleoenvironmental analysis and luminescence dating of upper Middle Pleistocene permafrost deposits of the Ulakhan Sular Formation, Adycha River, east Siberia

Ulakhan Sular provides one of the largest natural stratigraphic sections through ancient permafrost deposits in the Batagay-Betenkes region of the Yana Uplands of western Beringia, but their depositional environment, age, and paleoenvironmental significance are uncertain. To address these uncertainties, we report the results of reconnaissance observations of the stratigraphy, sedimentology, paleosols and soil-like bodies, plant and insect macrofossils, and geochronology of the permafrost deposits at the stratotype section of the Ulakhan Sular Formation. Sedimentologically, this formation is dominated by well-sorted, fine to very fine sand that contains fluvial, aeolian, and permafrost sedimentary structures consistent with deposition near the paleo-Adycha River. The fluvio-aeolian deposits have similarities and differences to periglacial fluvio-aeolian and aeolian deposits in modern arctic regions of Canada and Greenland, and Pleistocene deposits in Alaska, China, and northwest Europe. The remarkable thickness of aeolian deposits (∼50 m) at Ulakhan Sular is attributed to abundant local sand sources, ample accommodation space, and intensive aeolian transport and deposition. Optically stimulated luminescence dating of quartz sand and post-infrared-infrared dating of K-feldspar sand suggests deposition of the Ulakhan Sular Formation during late Marine Oxygen Isotope Stage (MIS) 6 or MIS 5. The aeolian sand-sheet deposits are correlated with other cold-climate aeolian sand and silt (loess) deposits in Beringia and southern Siberia, indicating a regional episode of aeolian sand transport and deposition at a similar time to glaciation by the Eastern Siberian Ice Sheet

A biomolecular perspective on mobile pastoralism and its role in wider socioeconomic connections in the Chalcolithic South Caucasus

Mobile pastoralism is widely evoked when discussing technological developments, resource procurement, trans-regional interactions, and exchange networks in the South Caucasus. In this study, we conduct a comprehensive multiproxy investigation of faunal and botanical remains from the Middle to Late Chalcolithic in southern Armenia, at the high altitude Yeghegis-1 site, to directly assess herd mobility and human subsistence practices. Our findings indicate that, alongside intensified interregional connectivity, the inhabitants practiced a rather sedentary form of multi-resource pastoralism, while maintaining herds at the site year-round. These results complement and expand upon models of pastoral mobility and its perceived crucial role in sustaining inter- and intraregional connectivity. We argue that alternative models of increased intra-regional connectivity, focused on exchange between different specialized settled economies, need to be considered and further research is essential to unravel the complex interplay between subsistence, trade, and socio-economic dynamics

Multifaceted analysis reveals diet and kinship of Late Pleistocene 'Tumat Puppies'

Distinguishing early domesticates from their wild progenitors presents a significant obstacle for understanding human-mediated effects in the past. The origin of dogs is particularly controversial because potential early dog remains often lack corroborating evidence that can provide secure links between proposed dog remains and human activity. The Tumat Puppies, two permafrost-preserved Late Pleistocene canids, have been hypothesized to have been littermates and early domesticates due to a physical association with putatively butchered mammoth bones. Through a combination of osteometry, stable isotope analysis, plant macrofossil analysis, and genomic and metagenomic analyses, this study exploits the unique properties of the naturally mummified Tumat Puppies to examine their familial relationship and to determine whether dietary information links them to human activities. The multifaceted analysis reveals that the 14,965-14,046 cal yr BP Tumat Puppies were littermates who inhabited a dry and relatively mild environment with heterogeneous vegetation and consumed a diverse diet, including woolly rhinoceros in their final days. However, because there is no evidence of mammoth consumption, these data do not establish a link between the canids and ancient humans