Search results for "78"
showing 10 items of 1163 documents
Determination of n-alkanes, polycyclic aromatic hydrocarbons and hopanes in atmospheric aerosol: evaluation and comparison of thermal desorption GC-M…
2019
Organic aerosol (OA) constitutes a large fraction of fine particulate matter (PM) in the urban air. However, the chemical nature and sources of OA are not well constrained. Quantitative analysis of OA is essential for understanding the sources and atmospheric evolution of fine PM, which requires accurate quantification of some organic compounds (e.g., markers). In this study, two analytical approaches, i.e., thermal desorption (TD) gas chromatography mass spectrometry (GC-MS) and solvent extract (SE) GC-MS, were evaluated for the determination of n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in ambient aerosol. For the SE approach, the recovery obtained is 89.3 %–101…
Bromine speciation in volcanic plumes: new in situ derivatization LC-MS method for the determination of gaseous hydrogen bromide by gas diffusion den…
2020
The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Monitoring of BrO/SO2-ratios has recently been correlated with changes in the activity of a volcano. BrO and SO2 can both be measured autonomously and simultaneously with the same instruments from a safe distance, making their ratio potentially a strong monitoring tool. However, BrO is not a primary emitted volcanic volatile and there exist still uncertainties about the formation of BrO in volcanic plumes, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. This study describes a new method for the determination of the BrO precursor, the ga…
"Para vestir a Borges a la italiana"
2021
Traducción de una nota de Juan José Mendoza publicada en la revista "Ñ Literatura", del diario argentino "Clarín" (18/09/2020).
Combined proton NMR wideline and NMR relaxometry to study SOM-water interactions of cation-treated soils
2013
Abstract Focusing on the idea that multivalent cations affect SOM matrix and surface, we treated peat and soil samples by solutions of NaCl, CaCl2 or AlCl3. Water binding was characterized with low field 1H-NMR-relaxometry (20 MHz) and 1H wideline NMR spectroscopy (400 MHz) and compared to contact angles. From 1H wideline, we distinguished mobile water and water involved in water molecule bridges (WaMB). Large part of cation bridges (CaB) between SOM functional groups are associated with WaMB. Unexpectedly, 1H NMRrelaxometry relaxation rates suggest that cross-linking in the Al-containing peat is not stronger than that by Ca. The relation between percentage of mobile water and WaMB water in…
Brief an Garlieb H. Merkel
1798
Ms. 930a, Nr. 12, Bl. 31r-34v Johannes Daniel Falk. Brief an Garlieb H. Merkel, Weimar, den 3. December 179[8?] Autora rokraksts / Autograph, vācu val. / Deutsch [8] lpp. / S. Attēlu numuri / Bildnummern: 930a-012-1, 930a-012-2-3, 930a-012-4-5, 930a-012-6-7, 930a-012-8 Im vorliegenden Brief vermischen sich private und berufliche Angelegenheiten sowie Klatsch miteinander. Nachdem Falk seine lange Antwortzeit zunächst damit begründet, dass er Merkels aktuelle Adresse nicht kenne, bringt er Neuigkeiten von der Krankheit einer nicht näher benannten Kammerrätin und nimmt an deren Leiden rege Anteil. Direkt im Anschluss präsentiert Falk den Stand seiner Verhandlungen mit Verlegern. Auch wenn Falk…
Las representaciones del saber académico: Aportaciones desde la Geografía Escolar
2019
When we talk with basic education´s teachers there is an impression in the case of learning Social Sciences, and Geography in particular that these sciences are not useful for the explanation of socio-environmental and daily problems. In this research, improvement proposals are sought so that students are motivated to learn about these problems. Based on two case studies such as flood risks (and their relationship with climate change) and the problems of the rural areas, the possibilities of combining motivation for learning close to personal emotions and with their own rigor have been explored of the conceptual explanation. To validate these results, quantitative and qualitative research t…
Evaluating the Effects of Sediment Transport on Pipe Flow Resistance
2021
In this paper, the applicability of a theoretical flow resistance law to sediment-laden flow in pipes is tested. At first, the incomplete self-similarity (ISS) theory is applied to deduce the velocity profile and the corresponding flow resistance law. Then the available database of measurements carried out by clear water and sediment-laden flows with sediments having a quasi-uniform sediment size and three different values of the mean particle diameter Dm (0.88 mm, 0.41 mm and 0.30 mm) are used to calibrate the Γ parameter of the power-velocity profile. The fitting of the measured local velocity to the power distribution demonstrates that (i) for clear flow the exponent δ can be estimated b…
Resonance between Cantor sets
2007
Let $C_a$ be the central Cantor set obtained by removing a central interval of length $1-2a$ from the unit interval, and continuing this process inductively on each of the remaining two intervals. We prove that if $\log b/\log a$ is irrational, then \[ \dim(C_a+C_b) = \min(\dim(C_a) + \dim(C_b),1), \] where $\dim$ is Hausdorff dimension. More generally, given two self-similar sets $K,K'$ in $\RR$ and a scaling parameter $s>0$, if the dimension of the arithmetic sum $K+sK'$ is strictly smaller than $\dim(K)+\dim(K') \le 1$ (``geometric resonance''), then there exists $r<1$ such that all contraction ratios of the similitudes defining $K$ and $K'$ are powers of $r$ (``algebraic resonance…
Generalized Lebesgue points for Sobolev functions
2017
In this article, we show that a function $f\in M^{s,p}(X),$ $0<s\leq 1,$ $0<p<1,$ where $X$ is a doubling metric measure space, has generalized Lebesgue points outside a set of $\mathcal{H}^h$-Hausdorff measure zero for a suitable gauge function $h.$
Subsurface flow and large-scale lateral saturated soil hydraulic conductivity in a Mediterranean hillslope with contrasting land uses
2017
Abstract The lateral saturated hydraulic conductivity, Ks,l , is the soil property that mostly governs subsurface flow in hillslopes. Determinations of Ks,l at the hillslope scale are expected to yield valuable information for interpreting and modeling hydrological processes since soil heterogeneities are functionally averaged in this case. However, these data are rare since the experiments are quite difficult and costly. In this investigation, that was carried out in Sardinia (Italy), large-scale determinations of Ks,l were done in two adjacent hillslopes covered by a Mediterranean maquis and grass, respectively, with the following objectives: i) to evaluate the effect of land use change o…