The Marine20 radiocarbon (14C) age calibration curve, and all earlier marine 14C calibration curves from the IntCal group, must be used extremely cautiously for the calibration of marine 14C samples from polar regions (outside ∼ 40ºS–40ºN) during glacial periods. Calibrating polar 14C marine samples from glacial periods against any Marine calibration curve (Marine20 or any earlier product) using an estimate of ${\rm{\Delta R}}$, the regional 14C depletion adjustment, that has been obtained from samples in the recent (non-glacial) past is likely to lead to bias and overconfidence in the calibrated age. We propose an approach to calibration that aims to address this by accounting for the possibility of additional, localized, glacial 14C depletion in polar oceans. We suggest, for a specific polar location, bounds on the value of ${\rm{\Delta }}{{\rm{R}}_{20}}\left( {\rm{\theta }} \right)$ during a glacial period. The lower bound ${\rm{\Delta R}}_{20}^{{\rm{Hol}}}$ may be based on 14C samples from the recent non-glacial (Holocene) past and corresponds to a low-depletion glacial scenario. The upper bound, ${\rm{\Delta R}}_{20}^{{\rm{GS}}}$, representing a high-depletion scenario is found by increasing ${\rm{\Delta R}}_{20}^{{\rm{Hol}}}$ according to the latitude of the 14C sample to be calibrated. The suggested increases to obtain ${\rm{\Delta R}}_{20}^{{\rm{GS}}}$ are based upon simulations of the Hamburg Large Scale Geostrophic Ocean General Circulation Model (LSG OGCM). Calibrating against the Marine20 curve using the upper and lower ${\rm{\Delta }}{{\rm{R}}_{20}}$ bounds provide estimates of calibrated ages for glacial 14C samples in high- and low-depletion scenarios which should bracket the true calendar age of the sample. In some circumstances, users may be able to determine which depletion scenario is more appropriate using independent paleoclimatic or proxy evidence.

Radiocarbon (14C) concentrations in the oceans are different from those in the atmosphere. Understanding these ocean-atmospheric 14C differences is important both to estimate the calendar ages of samples which obtained their 14C in the marine environment, and to investigate the carbon cycle. The Marine20 radiocarbon age calibration curve is created to address these dual aims by providing a global-scale surface ocean record of radiocarbon from 55,000–0 cal yr BP that accounts for the smoothed response of the ocean to variations in atmospheric 14C production rates and factors out the effect of known changes in global-scale palaeoclimatic variables. The curve also serves as a baseline to study regional oceanic 14C variation. Marine20 offers substantial improvements over the previous Marine13 curve. In response to community questions, we provide a short intuitive guide, intended for the lay-reader, on the construction and use of the Marine20 calibration curve. We describe the choices behind the making of Marine20, as well as the similarities and differences compared with the earlier Marine calibration curves. We also describe how to use the Marine20 curve for calibration and how to estimate ΔR—the localized variation in the oceanic 14C levels due to regional factors which are not incorporated in the global-scale Marine20 curve. To aid understanding, illustrative worked examples are provided.

The snow surface roughness at centimetre and millimetre scales is an important parameter related to wind transport, snowdrifts, snowfall, snowmelt and snow grain size. Knowledge of the snow surface roughness is also of high interest for analyzing the signal from radar sensors such as SAR, altimeters and scatterometers. Unfortunately, this parameter has seldom been measured over snow surfaces. The techniques used to measure the roughness of other surfaces, such as agricultural or sand soils, are difficult to implement in polar regions because of the harsh climatic conditions. In this paper we develop a device based on a laser profiler coupled with a GPS receiver on board a snowmobile. This instrumentation was tested successfully in midre Lovénbreen, Svalbard, in April 2006. It allowed us to generate profiles of 3 km sections of the snow-covered glacier surface. Because of the motion of the snowmobile, the roughness signal is mixed with the snowmobile signal. We use a distance/frequency analysis (the empirical mode decomposition) to filter the signal. This method allows us to recover the snow surface structures of wavelengths between 4 and 50 cm with amplitudes of >1 mm. Finally, the roughness parameters of snow surfaces are retrieved. The snow surface roughness is found to be dependent on the scales of the observations. The retrieved RMS of the height distribution is found to vary between 0.5 and 9.2 mm, and the correlation length is found to be between 0.6 and 46 cm. This range of measurements is particularly well adapted to the analysis of GHz radar response on snow surfaces.

Recovery Ice Stream has multiple branches reaching far into the East Antarctic ice sheet. We use new airborne and ground-based geophysics to give the first comprehensive overview of the upper catchment and, by constraining the physical setting, to advance our understanding of the controlling mechanisms for the onset of fast flow. The 400 km wide ice stream extends towards the Recovery Subglacial Lakes, a region characterized by a crustal boundary, a change in bed roughness, a bedrock topographic step and four topographic basins (A–D), three of which (A–C) contain subglacial water. All these characteristics are considered potential causal mechanisms that contribute to the onset of fast flow. In Lakes B and C the subglacial water is located in basins with sharp downstream ridges, in contrast to the gently sloping ridge on the downstream margin of Lake A. The fastest-flowing branch of the ice stream emanates from Lake A. The presence of multiple causal mechanisms along the four Recovery Lakes allows us to identify basal water as a dominant factor for the onset of fast flow, but only if it is stored in a shallow-sided basin where it can lubricate the flow downstream. Relatively minor topographic barriers appear to inhibit streaming.

Archaeological data and research results are essential to addressing such fundamental questions as the origins of human culture; the origin, waxing, and waning of civilizations and cities; the response of societies to long-term climate changes; and the systemic relationships implicated in human-induced changes in the environment. However, we lack the capacity for acquiring, managing, analyzing, and synthesizing the data sets needed to address important questions such as these. We propose investments in computational infrastructure that would transform archaeology’s ability to advance research on the field’s most compelling questions with an evidential base and inferential rigor that have heretofore been impossible. At the same time, new infrastructure would make archaeological data accessible to researchers in other disciplines. We offer recommendations regarding data management and availability, cyberinfrastructure tool building, and social and cultural changes in the discipline. We propose funding synthetic case studies that would demonstrate archaeology’s ability to contribute to transdisciplinary research on long-term social dynamics and serve as a context for developing computational tools and analytical workflows that will be necessary to attack these questions. The case studies would explore how emerging research in computer science could empower this research and would simultaneously provide productive challenges for computer science research.

This article represents a systematic effort to answer the question, What are archaeology’s most important scientific challenges? Starting with a crowd-sourced query directed broadly to the professional community of archaeologists, the authors augmented, prioritized, and refined the responses during a two-day workshop focused specifically on this question. The resulting 25 “grand challenges” focus on dynamic cultural processes and the operation of coupled human and natural systems. We organize these challenges into five topics: (1) emergence, communities, and complexity; (2) resilience, persistence, transformation, and collapse; (3) movement, mobility, and migration; (4) cognition, behavior, and identity; and (5) human-environment interactions. A discussion and a brief list of references accompany each question. An important goal in identifying these challenges is to inform decisions on infrastructure investments for archaeology. Our premise is that the highest priority investments should enable us to address the most important questions. Addressing many of these challenges will require both sophisticated modeling and large-scale synthetic research that are only now becoming possible. Although new archaeological fieldwork will be essential, the greatest pay off will derive from investments that provide sophisticated research access to the explosion in systematically collected archaeological data that has occurred over the last several decades.

Contrastive phonology has been preoccupied with the phoneme concept and the isolated word. The Contrastive Structure Series demonstrates this quite clearly. In Moulton's contrastive comparison of English and German sounds (Moulton, 1962), to take a representative example of the series and of contrastive phonological studies in general, 107 pages out of 145 deal with the consonant and vowel phonemes in English and German words and with their contrastive analysis. Only 31 pages treat stress (largely word stress), intonation and the inevitable juncture, which is the epitome of word phonemics in that it looks at the incidence of boundary signals at word and morpheme boundaries, e.g. antrat and das Kitzeln with strongly aspirated stops as against Landrat and die Skizze with weakly aspirated or unaspirated stops indicating different divisions between word final and initial consonants (p. 142). I would like to mention in passing that this opposition is artificially constructed in word material by a linguist on the basis of the equally artificial codification in Siebs (de Boor et al., 1969), where again hardly any tribute is paid to segmental sentence phonology (Kohler, 1970).

Acute flaccid paralysis (AFP) surveillance data from India were analysed to examine sensitivity of poliovirus isolation from stool specimens and the added sensitivity obtained from collection of a second stool specimen. Analysis was restricted to Indian AFP cases, 1998–2000, with two adequate stool specimens. The proportion of cases confirmed with wild poliovirus isolation by the second specimen only was calculated, regardless of specimen quality. Overall specimen sensitivity (1998–2000) was 81% using the first specimen, 78% using the second, and 96% using both. Sensitivity increased from 1998 to 2000, with slightly higher sensitivity each year for the first specimen. The second specimen increased sensitivity by 15% overall and contributed more when the first specimen was collected late or was in poor condition. As wild poliovirus disappears, increased sensitivity provided by a second stool specimen may reduce the risk of missing circulating virus.

Cubic phase GaN/AlxGa1-xN Multi Quantum Well structures were grown by rf-plasma assisted molecular beam epitaxy (MBE) on GaAs (001) substrates. X-ray measurements showed a high phase purity of the epilayers and revealed an Aluminum incorporation between 9 % and 49 %, respectively. The QW luminescence was tuned between 3.25 eV and 3.4 eV by means of the variation of QW barrier Aluminum content and QW width. Strong Cathodoluminescence (CL) from the GaN QWs and the underlying cubic AlxGa1-xN bulk material was observed at room temperature. The spatial localization of the QW emission was unambiguously determined by depth-resolved CL measurements. Combined with a model of energy-dependent penetration, diffusion, and recombination, these variations indicate a value of about 20 nm for the minority carrier diffusion length within the AlxGa1-xN confinement layer. The assignment of AlxGa1-xN bulk and GaN luminescence was further supported by employing a simple effective-mass quantum mechanical model.

Recent results on the local bonding of nitrogen in dilute GaInAsN and AlGaAsN on GaAs are reviewed, revealing that bonding of nitrogen in GaInAsN is controlled by an interplay between bond cohesive energy and reduction of local strain. Thus, III-N bonding in GaInAsN can be changed from Ga-N to In-N by post-growth thermal annealing. In AlGaAsN, in contrast, nitrogen bonds preferentially to Al, i.e. Al-N bonds are formed, due to the much larger cohesive energy of the Al-N bond. Further, results on indium-rich highly strained GaInAsN quantum wells on InP substrate are reported, showing room-temperature photoluminescence at wavelengths up to 2.3 μm. This result demonstrates the potential of high indium content dilute GaInAsN for InP-based long wavelength diode lasers.

The optical properties of Carbon doped cubic GaN epilayers have been investigated by temperature and intensity dependent photoluminescence measurements. RF-plasma assisted molecular beam epitaxy equipped with an e-beam-evaporation source for carbon doping is used to grow the cubic GaN layers on GaAs (001) substrates. With increasing Carbon flux a new photoluminescence line at 3.08 eV appeared at 2K. This line is attributed to a donor acceptor transistion, which involves the shallow CN acceptor. From the spectral position the binding energy of the C acceptor is estimated to be about EC = 0.215 eV. Our experiments demonstrate that C indeed introduces a shallow acceptor in cubic GaN with an acceptor binding energy, which is about 15 meV lower than that observed for the Mg acceptor in cubic GaN. However, at high C fluxes a deep red luminescence band appeared at 2.1 eV, indicating compensation effects.

Spectroscopic ellipsometry (SE) has been used for the characterization of AlGaN/GaN and InGaN/GaN heterostructures. The resulting pseudodielectric function spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. From this analysis, the dielectric function spectra of GaN, AlxGa1−xN (x≤0.16), and In0.13Ga0.87N were deduced. Further, the dependence of the AlxGa1−xN band gap energy on the Al mole fraction was derived and compared with photoluminescence data recorded on the same material. The SE band gap data are compatible with a bowing parameter close to 1 eV for the composition dependence of the AlxGa1−xN gap energy. Finally, the parametric dielectric functions have been used to model the pseudodielectric function spectrum of a complete GaN/AlGaN/InGaN LED structure.