288 research outputs found
Exciting surface plasmons with transformation media
The final publication is available at Springer via http://dx.doi.org/10.1007/s11468-012-9361-5We present a way of exciting surface plasmon polaritons along non-patterned metallic surfaces by means of a flat squeezing slab designed with transformation optics. The slab changes the dispersion relation of incident light, enabling evanescent coupling to propagating surface plasmons. Unlike prism couplers, the proposed device does not introduce reflections at its input interface. Moreover, its compact geometry is suitable for integration. A feasible dielectric implementation of the coupler is suggested. Finally, we show that the angular response of the device can be engineered by using a non-uniform compression factor. As an example, we design a coupler with a half-power angular bandwidth 2. 5 times higher than that of a conventional dielectric coupler. © 2012 Springer Science+Business Media, LLC.Financial support by Spanish Ministerio de Ciencia e Innovacion (contracts CSD2008-00066 and TEC2008-06871-C02, and FPU grant) is gratefully acknowledged.GarcĂa Meca, C.; Ortuño Molinero, R.; MartĂ Sendra, J.; MartĂnez Abietar, AJ. (2012). Exciting surface plasmons with transformation media. Plasmonics. 7(4):701-707. https://doi.org/10.1007/s11468-012-9361-5S70170774Raether H (1988) Surface plasmons on smooth and rough surfaces and on gratings. Springer-Verlag, BerlinBarnes WL, Dereux A, Ebbesen TW (2003) Surface plasmon subwavelength optics. Nature 424:824â830Maier SA (2007) Plasmonics: fundamentals and applications. Springer, New YorkSchuller JA, Barnard ES, Cai W, Jun YC, White JS, Brongersma ML (2010) Plasmonics for extreme light concentration and manipulation. Nat Mater 9:193â204Brongersma ML, Shalaev VM (2010) The case for plasmonics. Science 328:440â441Liu Y, Zentgraf T, Bartal G, Zhang X (2010) Transformational plasmon optics. Nano Lett 10:1991â1997Huidobro PA, Nesterov ML, MartĂn-Moreno L, GarcĂa-Vidal FJ (2010) Transformation optics for plasmonics. Nano Lett 10:1985â1990Kadic M, Guenneau S, Enoch S (2010) Transformational plasmonics: cloak, concentrator and rotator for SPPs. Opt Express 18:12027â12032Zhang J, Xiao S, Wubs M, Mortensen NA (2011) Surface plasmon wave adapter designed with transformation optics. ACS Nano 5:4359â4364Pendry JB, Schurig D, Smith DR (2006) Controlling electromagnetic fields. Science 312:1780â1782Leonhardt U (2006) Optical conformal mapping. Science 312:1777â1780Leonhardt U, Philbin TG (2006) General relativity in electrical engineering. New J Phys 8:247Sambles JR, Bradbery GW, Yang F (1991) Optical excitation of surface plasmons: an introduction. Contemp Phys 32:173â183Rahm M, Roberts DA, Pendry JB, Smith DR (2008) Transformation-optical design of adaptive beam bends and beam expanders. Opt Express 16:11555â11567Vasic B, Isic G, Gajic R, Hingerl K (2009) Coordinate transformation based design of confined metamaterial structures. Phys Rev B 79:85103Tichit P, Burokur SN, Lustrac A (2009) Waveguide taper engineering using coordinate transformation technology. Opt Express 18:767â772Zang X, Jiang C (2010) Manipulating the field distribution via optical transformation. Opt Express 18:10168â10176GarcĂa-Meca C, Tung MM, GalĂĄn JV, Ortuño R, RodrĂguez-Fortuño FJ, MartĂ J, MartĂnez A (2011) Squeezing and expanding light without reflections via transformation optics. Opt Express 19:3562â3575Li J, Han S, Zhang S, Bartal G, Zhang X (2009) Designing the Fourier space with transformation optics. Opt Lett 34:3128â3130Li J, Pendry JB (2008) Hiding under the carpet: a new strategy for cloaking. Phys Rev Lett 101:20390
Role of AMP-Activated Protein Kinase on Steroid Hormone Biosynthesis in Adrenal NCI-H295R Cells
Regulation of human androgen biosynthesis is poorly understood. However, detailed knowledge is needed to eventually solve disorders with androgen dysbalance. We showed that starvation growth conditions shift steroidogenesis of human adrenal NCI-H295R cells towards androgen production attributable to decreased HSD3B2 expression and activity and increased CYP17A1 phosphorylation and 17,20-lyase activity. Generally, starvation induces stress and energy deprivation that need to be counteracted to maintain proper cell functions. AMP-activated protein kinase (AMPK) is a master energy sensor that regulates cellular energy balance. AMPK regulates steroidogenesis in the gonad. Therefore, we investigated whether AMPK is also a regulator of adrenal steroidogenesis. We hypothesized that starvation uses AMPK signaling to enhance androgen production in NCI-H295R cells. We found that AMPK subunits are expressed in NCI-H295 cells, normal adrenal tissue and human as well as pig ovary cells. Starvation growth conditions decreased phosphorylation, but not activity of AMPK in NCI-H295 cells. In contrast, the AMPK activator 5-aminoimidazole-4-carboxamide (AICAR) increased AMPKα phosphorylation and increased CYP17A1-17,20 lyase activity. Compound C (an AMPK inhibitor), directly inhibited CYP17A1 activities and can therefore not be used for AMPK signaling studies in steroidogenesis. HSD3B2 activity was neither altered by AICAR nor compound C. Starvation did not affect mitochondrial respiratory chain function in NCI-H295R cells suggesting that there is no indirect energy effect on AMPK through this avenue. In summary, starvation-mediated increase of androgen production in NCI-H295 cells does not seem to be mediated by AMPK signaling. But AMPK activation can enhance androgen production through a specific increase in CYP17A1-17,20 lyase activity
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
Azimuthal anisotropy of charged particles at high transverse momenta in PbPb collisions at sqrt(s[NN]) = 2.76 TeV
The azimuthal anisotropy of charged particles in PbPb collisions at
nucleon-nucleon center-of-mass energy of 2.76 TeV is measured with the CMS
detector at the LHC over an extended transverse momentum (pt) range up to
approximately 60 GeV. The data cover both the low-pt region associated with
hydrodynamic flow phenomena and the high-pt region where the anisotropies may
reflect the path-length dependence of parton energy loss in the created medium.
The anisotropy parameter (v2) of the particles is extracted by correlating
charged tracks with respect to the event-plane reconstructed by using the
energy deposited in forward-angle calorimeters. For the six bins of collision
centrality studied, spanning the range of 0-60% most-central events, the
observed v2 values are found to first increase with pt, reaching a maximum
around pt = 3 GeV, and then to gradually decrease to almost zero, with the
decline persisting up to at least pt = 40 GeV over the full centrality range
measured.Comment: Replaced with published version. Added journal reference and DO
Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy
A search for new physics is performed in events with two same-sign isolated
leptons, hadronic jets, and missing transverse energy in the final state. The
analysis is based on a data sample corresponding to an integrated luminosity of
4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of
7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of
140 increase in integrated luminosity over previously published results. The
observed yields agree with the standard model predictions and thus no evidence
for new physics is found. The observations are used to set upper limits on
possible new physics contributions and to constrain supersymmetric models. To
facilitate the interpretation of the data in a broader range of new physics
scenarios, information on the event selection, detector response, and
efficiencies is provided.Comment: Published in Physical Review Letter
Measurement of jet fragmentation into charged particles in pp and PbPb collisions at sqrt(s[NN]) = 2.76 TeV
Jet fragmentation in pp and PbPb collisions at a centre-of-mass energy of
2.76 TeV per nucleon pair was studied using data collected with the CMS
detector at the LHC. Fragmentation functions are constructed using
charged-particle tracks with transverse momenta pt > 4 GeV for dijet events
with a leading jet of pt > 100 GeV. The fragmentation functions in PbPb events
are compared to those in pp data as a function of collision centrality, as well
as dijet-pt imbalance. Special emphasis is placed on the most central PbPb
events including dijets with unbalanced momentum, indicative of energy loss of
the hard scattered parent partons. The fragmentation patterns for both the
leading and subleading jets in PbPb collisions agree with those seen in pp data
at 2.76 TeV. The results provide evidence that, despite the large parton energy
loss observed in PbPb collisions, the partition of the remaining momentum
within the jet cone into high-pt particles is not strongly modified in
comparison to that observed for jets in vacuum.Comment: Submitted to the Journal of High Energy Physic
Structure of Human DNA Polymerase Îș Inserting dATP Opposite an 8-OxoG DNA Lesion
Background: Oxygen-free radicals formed during normal aerobic cellular metabolism attack bases in DNA and 7,8-dihydro-8-oxoguanine (8-oxoG) is one of the major lesions formed. It is amongst the most mutagenic lesions in cells because of its dual coding potential, wherein 8-oxoG(syn) can pair with an A in addition to normal base pairing of 8-oxoG(anti) with a C. Human DNA polymerase Îș (PolÎș) is a member of the newly discovered Y-family of DNA polymerases that possess the ability to replicate through DNA lesions. To understand the basis of PolÎș\u27s preference for insertion of an A opposite 8-oxoG lesion, we have solved the structure of PolÎș in ternary complex with a template-primer presenting 8-oxoG in the active site and with dATP as the incoming nucleotide.
Methodology and Principal Findings: We show that the PolÎș active site is well-adapted to accommodate 8-oxoG in the syn conformation. That is, the polymerase and the bound template-primer are almost identical in their conformations to that in the ternary complex with undamaged DNA. There is no steric hindrance to accommodating 8-oxoG in the syn conformation for Hoogsteen base-paring with incoming dATP.
Conclusions and Significance: The structure we present here is the first for a eukaryotic translesion synthesis (TLS) DNA polymerase with an 8-oxoG:A base pair in the active site. The structure shows why PolÎș is more efficient at inserting an A opposite the 8-oxoG lesion than a C. The structure also provides a basis for why PolÎș is more efficient at inserting an A opposite the lesion than other Y-family DNA polymerases
Increasing Protein at the Expense of Carbohydrate in the Diet Down-Regulates Glucose Utilization as Glucose Sparing Effect in Rats
High protein (HP) diet could serve as a good strategy against obesity, provoking the changes in energy metabolic pathways. However, those modifications differ during a dietary adaptation. To better understand the mechanisms involved in effect of high protein diet (HP) on limiting adiposity in rats we studied in parallel the gene expression of enzymes involved in protein and energy metabolism and the profiles of nutrients oxidation. Eighty male Wistar rats were fed a normal protein diet (NP, 14% of protein) for one week, then either maintained on NP diet or assigned to a HP diet (50% of protein) for 1, 3, 6 and 14 days. mRNA levels of genes involved in carbohydrate and lipid metabolism were measured in liver, adipose tissues, kidney and muscles by real time PCR. Energy expenditure (EE) and substrate oxidation were measured by indirect calorimetry. Liver glycogen and plasma glucose and hormones were assayed. In liver, HP feeding 1) decreased mRNA encoding glycolysis enzymes (GK, L-PK) and lipogenesis enzymes(ACC, FAS), 2) increased mRNA encoding gluconeogenesis enzymes (PEPCK), 3) first lowered, then restored mRNA encoding glycogen synthesis enzyme (GS), 4) did not change mRNA encoding ÎČ-oxidation enzymes (CPT1, ACOX1, ÎČHAD). Few changes were seen in other organs. In parallel, indirect calorimetry confirmed that following HP feeding, glucose oxidation was reduced and fat oxidation was stable, except during the 1st day of adaptation where lipid oxidation was increased. Finally, this study showed that plasma insulin was lowered and hepatic glucose uptake was decreased. Taken together, these results demonstrate that following HP feeding, CHO utilization was increased above the increase in carbohydrate intake while lipogenesis was decreased thus giving a potential explanation for the fat lowering effect of HP diets
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