908 research outputs found
Insights into Tikhonov regularization: application to trace gas column retrieval and the efficient calculation of total column averaging kernels
Insights are given into Tikhonov regularization and its application
to the retrieval of vertical column densities of atmospheric trace
gases from remote sensing measurements. The study builds upon the
equivalence of the least-squares profile-scaling approach and
Tikhonov regularization method of the first kind with an infinite
regularization strength. Here, the vertical profile is expressed
relative to a reference profile. On the basis of this, we propose a
new algorithm as an extension of the least-squares profile scaling
which permits the calculation of total column averaging kernels on
arbitrary vertical grids using an analytic expression. Moreover, we
discuss the effective null space of the retrieval, which comprises
those parts of a vertical trace gas distribution which cannot be
inferred from the measurements.
Numerically the algorithm
can be implemented in a robust and efficient manner. In particular
for operational data processing with challenging demands on
processing time, the proposed inversion method in combination with
highly efficient forward models is an asset. For demonstration
purposes, we apply the algorithm to CO column retrieval from
simulated measurements in the 2.3 ÎĽm spectral region and
to O<sub>3</sub> column retrieval from the UV. These represent ideal
measurements of a series of spaceborne spectrometers such as
SCIAMACHY, TROPOMI, GOME, and GOME-2. For both spectral ranges, we
consider clear-sky and cloudy scenes where clouds are modelled as an
elevated Lambertian surface. Here, the smoothing error for the
clear-sky and cloudy atmosphere is significant and reaches several
percent, depending on the reference profile which is used for
scaling. This underlines the importance of the column averaging
kernel for a proper interpretation of retrieved column densities.
Furthermore, we show that the smoothing due to regularization can be
underestimated by calculating the column averaging kernel on a too
coarse vertical grid. For both retrievals, this effect becomes
negligible for a vertical grid with 20–40 equally thick layers
between 0 and 50 km
Appearance of Flat Bands and Edge States in Boron-Carbon-Nitride Nanoribbons
Presence of flat bands and edge states at the Fermi level in graphene
nanoribbons with zigzag edges is one of the most interesting and attracting
properties of nanocarbon materials but it is believed that they are quite
fragile states and disappear when B and N atoms are doped at around the edges.
In this paper, we theoretically investigate electronic and magnetic properties
of boron-carbon-nitride (BCN) nanoribbons with zigzag edges where the outermost
C atoms on the edges are alternately replaced with B and N atoms using the
first principles calculations. We show that BCN nanoribbons have the flat bands
and edge states at the Fermi level in both H_2 rich and poor environments. The
flat bands are similar to those at graphene nanoribbons with zigzag edges, but
the distributions of charge and spin densities are different between them. A
tight binding model and the Hubbard model analysis show that the difference in
the distribution of charge and spin densities is caused by the different site
energies of B and N atoms compared with C atoms.Comment: 5 pages; 3 figure
Expression Patterns of BDNF with Central Anorexigenic Signaling Pathways Involving PACAP in the Hypothalamic Ventromedial Nuclei
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid polypeptide belonging to the secretin super family of peptides. PACAP binds to its type 1 receptor (PAC1R) with greater affinity than for the receptors for vasoactive intestinal polypeptides (VIP), VPAC1 and VPAC2. Although mRNA for PACAP and its receptor PAC1R are found throughout the central nervous system, they are abundantly expressed in the hypothalamic ventromedial nuclei (VMN). In male Sprague Dawley rats, infusions of PACAP into the VMN produce a robust decrease in food intake with concomitant increased energy expenditure, decreased body weight, and significantly elevated brain-derived neurotrophic factor (BDNF) mRNA expression in the VMN. This latter effect of PACAP on BDNF mRNA expression has been shown to occur in other brain regions. Exogenous BDNF in the VMN regulates energy homeostasis in a manner similar to that of PACAP with decreased feeding and increased metabolism. Although the physiological responses to individual PACAP and BDNF infusions in the VMN lead to decreased feeding behavior and body weight loss, the anatomical distribution of these two cell signals in the VMN has not been established. PACAP-induced changes in BDNF mRNA expression in the VMN may reveal an important interaction with PACAP signaling in the control of feeding behavior. In the present study, we have employed double-labeled fluorescent in-situ hybridization (FISH) to examine the expression patterns of PACAP, PAC1R and BDNF mRNA containing neuronal cells. In the VMN, PACAP mRNA expressing cells co-express BDNF, PAC1R, and VGLUT2. BDNF mRNA expressing cells co-express PAC1R and PACAP. Coupled with previous behavioral data demonstrating PACAP- and BDNF-induced changes in feeding behavior, the co-expression of BDNF with PACAP and PAC1R mRNA in the VMN suggest a potential functional relationship between the two signaling peptides in the regulation of energy homeostasis. The specific and integrated contributions of PACAP and BDNF in the VMN towards regulating energy homeostasis and feeding behavior still remain to be studied
Experimentally Engineering the Edge Termination of Graphene Nanoribbons
The edges of graphene nanoribbons (GNRs) have attracted much interest due to
their potentially strong influence on GNR electronic and magnetic properties.
Here we report the ability to engineer the microscopic edge termination of high
quality GNRs via hydrogen plasma etching. Using a combination of
high-resolution scanning tunneling microscopy and first-principles
calculations, we have determined the exact atomic structure of plasma-etched
GNR edges and established the chemical nature of terminating functional groups
for zigzag, armchair and chiral edge orientations. We find that the edges of
hydrogen-plasma-etched GNRs are generally flat, free of structural
reconstructions and are terminated by hydrogen atoms with no rehybridization of
the outermost carbon edge atoms. Both zigzag and chiral edges show the presence
of edge states.Comment: 16+9 pages, 3+4 figure
Biomechanical analysis of temporomandibular joint dynamics based on real-time magnetic resonance imaging
Aim: The traditional hinge axis theory of temporomandibular joint (TMJ) dynamics is increasingly being replaced by the theory of instantaneous centers of rotation (ICR). Typically, ICR determinations are based on theoretical calculations or three-dimensional approximations of finite element models. Materials and methods: With the advent of real-time magnetic resonance imaging (MRI), natural physiologic movements of the TMJ may be visualized with 15 frames per second. The present study employs real-time MRI to analyze the TMJ biomechanics of healthy volunteers during mandibular movements, with a special emphasis on horizontal condylar inclination (HCI) and ICR pathways. The Wilcoxon rank sum test was used to comparatively analyze ICR pathways of mandibular opening and closure. Results: Mean HCI was 34.8 degrees (± 11.3 degrees) and mean mandibular rotation was 26.6 degrees (± 7.2 degrees). Within a mandibular motion of 10 to 30 degrees, the resulting x- and y-translation during opening and closure of the mandible differed significantly (10 to 20 degrees, x: P = 0.02 and y: P 30 degrees showed no significant differences in x- and y-translation. Near occlusion movements differed only for y-translation (P < 0.01). Conclusion: Real-time MRI facilitates the direct recording of TMJ structures during physiologic mandibular movements. The present findings support the theory of ICR. Statistics confirmed that opening and closure of the mandible follow different ICR pathways, which might be due to muscular activity discrepancies during different movement directions. ICR pathways were similar within maximum interincisal distance (MID) and near occlusion (NO), which might be explained by limited extensibility of tissue fibers (MID) and tooth contact (NO), respectively
Gender differences in climate change perception and adaptation strategies: A case study on three provinces in Vietnam’s Mekong River Delta
This brief summarizes the findings of a project output for the Policy Information and Response Platform on Climate Change and Rice in ASEAN and its Member Countries (PIRCCA), being implemented by the International Rice Research Institute (IRRI). The report focuses on the results of the survey conducted in the first half of 2015 on climate change perception and adaptation strategies of male and female farmers in three selected provinces across the Mekong River Delta (MRD) region in Vietnam: An Giang, Bac Lieu, and Tra Vihn. The survey gathered information on current climate change perceptions and adaptation strategies and gaps between the identified male and female respondents
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