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Soil CO2 flux measurement is a key method that can be used to monitor the hazards in an active volcanic area. In order to determine accurately the variations of the CO2 soil emission we propose an approach based on the radiocarbon (14C) deficiency recorded in the plants grown in and around the Solfatara (Naples, Italy). We twice sampled selected poaceae plants in 17 defined sites around the Solfatara volcano. 14C measurements by liquid scintillation counting (LSC) were achieved on the grass samples. The 14C deficiency determined in the sampled plants, compared to the atmosphere 14C activity, ranged from 6.6 to 51.6%. We then compared the proportion of magmatic CO2 inferred to the instantaneous measurements of CO2 fluxes from soil performed by the accumulation chamber CO2 degassing measurement at the moment of the sampling at each site. The results show a clear correlation (r=0.88) between soil CO2 fluxes and 14C activity. The determination of the plants 14C deficiency provides an estimate of the CO2 rate within a few square meters, integrating CO2 soil degassing variations and meteorological incidences over a few months. It can therefore become an efficient bio-sensor and can be used as a proxy to cartography of the soil CO2 and to determine its variations through time
The Cave of Pan is located on the N/NE slope of the hill of Oinoe (38°09′31.60′′N, 23°55′48.60′′E), west of modern Marathon. In rescue excavation campaigns during the last three years, among other finds, charcoal and seashell samples were also collected. The purpose of this study is the accelerator mass spectrometry (AMS) dating of the cave’s anthropogenic deposits and the calculation of the regional marine reservoir effect during the Neolithic period. For that purpose, 7 charcoal pieces and 1 seashell were dated. Our results show that the cave was used from the second quarter of the 6th millennium (Middle Neolithic period) until the beginning of the 5th millennium BC. Additionally, one sample collected from a depth of 2 cm from the present surface of the cave yielded an age falling within the 6th century AD, giving thus the absolute time span of the cave use. Moreover, the radiocarbon (14C) ages of one pair of charcoal-seashell samples showed that the marine reservoir age R(t) in the estuarine Marathon Bay region during the 5th millennium BC is 775±57 yr and the local sea surface reservoir deviation ΔR is found to be 402±63 14C yr (within 1σ).
We show that if a collection of lines in a vector space over a finite field has “dimension” at least
, then its union has “dimension” at least
. This is the sharp estimate of its type when no structural assumptions are placed on the collection of lines. We also consider some refinements and extensions of the main result, including estimates for unions of
The Chauvet-Pont d'Arc Cave is one of the most important sites for the study of the earliest manifestations and development of prehistoric art at the beginning of the Upper Paleolithic. Different dating techniques have been performed thus far (AMS 14C, U/Th TIMS, 36Cl dating) to model the chronological framework of this decorated cave. The cave yielded several large charcoal fragments, which enabled the opportunity for obtaining multiple dates; thus, a First Radiocarbon Intercomparison Program (FIP) was initiated in 2004 using three charcoal pieces. The FIP demonstrated that those cross-dated samples belonged to a time period associated with the first human occupation. One of the statistical interests of an intercomparison program is to reduce the uncertainty on the sample age; thus, to further assess the accuracy of the chronological framework, the Second Intercomparison Program (SIP) involving 10 international 14C laboratories was carried out on two pieces of charcoal found inside two hearth structures of the Galerie des Mégacéros. Each laboratory used its own pretreatment and AMS facilities. In total, 21 and 22 measurements were performed, respectively, which yielded consistent results averaging ∼32 ka BP. Two strategies have currently been developed to identify statistical outliers and to deal with them; both lead to quasi-identical calibrated combined densities. Finally, the new results were compared with those of the FIP, leading to the important conclusion that five different samples from at least three different hearth structures give really tightened temporal densities, associated with one short human occupation in the Galerie des Mégacéros.
We prove weak-type
$\left( 1,\,1 \right)$
estimates for compositions of maximal operators with singular integrals. Our main object of interest is the operator
$\Delta *\Psi $
is Bourgain’s maximal multiplier operator and
is the sum of several modulated singular integrals; here our method yields a significantly improved bound for the
operator norm when
. We also consider associated variation-norm estimates.
Tells famously capture the historical sequences of the earliest farmers—but digging them is not easy. With a depth of strata of 17m at Dikili Tash, the earliest occupation was out of reach of a trench. But our researchers got there by coring, extending the date of the first occupation back 1000 years, and deducing, from small samples, the changing environment and possible connections with Anatolia.
We establish a mixed norm estimate for the Radon transform in
when the set of directions has fractional dimension. This estimate is used to prove a result about an exceptional set of directions connected with projections of planar sets. That leads to a conjecture analogous to a well-known conjecture of Furstenberg.
Using the polynomial method of Dvir [On the size of Kakeya sets in finite fields. Preprint], we establish optimal estimates for Kakeya sets and Kakeya maximal functions associated to algebraic varieties W over finite fields F. For instance, given an (n−1)-dimensional projective variety W⊂¶n(F), we establish the Kakeya maximal estimate for all functions f:Fn→R and d≥1, where for each w∈W, the supremum is over all irreducible algebraic curves in Fn of degree at most d that pass through w but do not lie in W, and with Cn,W,d depending only on n,d and the degree of W; the special case when W is the hyperplane at infinity in particular establishes the Kakeya maximal function conjecture in finite fields, which in turn strengthens the results of Dvir.
We consider the Fourier restriction operators associated to certain degenerate curves in ℝd for which the highest torsion vanishes. We prove estimates with respect to affine arclength and with respect to the Euclidean arclength measure on the curve. The estimates have certain uniform features, and the affine arclength results cover families of flat curves.
We present the first results of an accelerator mass spectrometry (AMS) radiocarbon intercomparison program on 3 different charcoal samples collected in one of the hearths of the Megaceros gallery of Chauvet Cave (Ardèche, France). This cave, rich in parietal decoration, is important for the study of the appearance and evolution of prehistoric art because certain drawings have been 14C dated to the Aurignacian period at the beginning of the Upper Paleolithic. The new dates indicate an age of about 32,000 BP, which is consistent with this attribution and in agreement with the results from the same sector of the cave measured previously at the Laboratoire des Sciences du Climat et de l'Environnement (LSCE). Six laboratories were involved in the intercomparison. Samples were measured in 4 AMS facilities: Center for Isotope Research, Groningen University, the Netherlands; the Oxford Radiocarbon Accelerator Unit, UK; the Centre de datation par le carbone 14, Univ. Claude Bernard Lyon 1, France (measured by AMS facilities of Poznań University, Poland); and the LSCE, UMR CEA-CNRS-UVSQ, France (measured by the Leibniz-Labor of Christian-Albrechts-Universität Kiel, Germany).
I deficiency is the leading cause of preventable mental retardation. A number of surveys in Afghanistan show goitre prevalence rates more than 20% amongst children and women. Access to iodised salt remains low, with disparate coverage by region, despite the recent implementation of a national salt iodisation programme. The objectives were to identify whether the presence of goitre is a satisfactory marker of I deficiency and to examine the relationship between goitre and thyroid function. A case–control study was carried out in children and women of childbearing age, stratified on the presence of goitre. Adequate levels of urinary I were observed in 6·8% of all the subjects, and amongst the subjects without goitre, this figure was only 9%. The presence of goitre was significantly associated with severe urinary I deficiency; however, the difference between the cases and controls was not as great as expected. An association between the presence of goitre and elevated thyroid-stimulating hormone (TSH) levels was observed, but 14% of the children without palpable goitre also showed abnormal TSH levels.Given that the majority of subjects showed some degree of I deficiency and that children without goitre may have elevated TSH levels, the absence of goitre is an insufficient indicator to determine adequate I status. The risk of subsequent development of goitre, in the currently non-goitre population, is elevated. This suggests that short-term I supplementation should be considered independently of the presence of goitre or urinary I level, until the access to and consumption of iodised salt is generalised.
Let S be a smooth hypersurface in ℝn
with surface area measure ds and Gaussian
curvature κ(s). Define the convolution operator T by
for suitable functions f on ℝn. We are interested in the
Lp − Lq mapping properties of T.
Write [Sscr ] for the type set of T, the set
It is well known (see, e.g. [O1]) that [Sscr ] is contained in the closed triangle [Tscr ] with
vertices (0, 0), (1, 1) and (n/(n+1), 1/(n+1)). This paper is concerned with estimates
of the form
The estimate (1) is interesting because it serves as a weak substitute for the
L(n+1)/n − Ln+1 boundedness of T.
For example, if S is compact and (1) holds, then well-known arguments show that [Sscr ] differs from the
full triangle [Tscr ] by at most the point (n/(n + 1), 1/(n + 1)). Our main
result is a condition sufficient to imply (1). Its statement requires the following definition.
Various polyimide films (Kapton, Upilex, Novax, and PPT) were carbonized and graphitized up to 3000 °C. They were studied by optical and electron microscopies. All films retaining oxygen as a cross linker over 1000 °C, i.e., Kapton, Upilex, and Novax, graphitize as anthracites (high rank coals) do. They get a long range statistical orientation parallel to the film plane with a nanotexture of flattened pores. Graphitization is both sudden and perfect above 2100 °C when the pore walls break. Since oxygen is released at 1000 °C, the film PPT behaves as a compact nonporous graphitizing carbon (orientation parallel to the film plane). Thermal graphitization is progressive and begins at a higher temperature.