Effective degrees of nonlinearity in a family of generalized models of two-dimensional turbulence

We study the small-scale behavior of generalized two-dimensional turbulence governed by a family of model equations, in which the active scalar $\theta=(-\Delta)^{\alpha/2}\psi$ is advected by the incompressible flow $\u=(-\psi_y,\psi_x)$. The dynamics of this family are characterized by the material conservation of $\theta$, whose variance is preferentially transferred to high wave numbers. As this transfer proceeds to ever-smaller scales, the gradient $\nabla\theta$ grows without bound. This growth is due to the stretching term $(\nabla\theta\cdot\nabla)\u$ whose ``effective degree of nonlinearity'' differs from one member of the family to another. This degree depends on the relation between the advecting flow $\u$ and the active scalar $\theta$ and is wide ranging, from approximately linear to highly superlinear. Linear dynamics are realized when $\nabla\u$ is a quantity of no smaller scales than $\theta$, so that it is insensitive to the direct transfer of the variance of $\theta$, which is nearly passively advected. This case corresponds to $\alpha\ge2$, for which the growth of $\nabla\theta$ is approximately exponential in time and non-accelerated. For $\alpha<2$, superlinear dynamics are realized as the direct transfer of entails a growth in \nabla\u, thereby enhancing the production of $\nabla\theta$. This superlinearity reaches the familiar quadratic nonlinearity of three-dimensional turbulence at $\alpha=1$ and surpasses that for $\alpha<1$. The usual vorticity equation ($\alpha=2$) is the border line, where \nabla\u and $\theta$ are of the same scale, separating the linear and nonlinear regimes of the small-scale dynamics. We discuss these regimes in detail, with an emphasis on the locality of the direct transfer.Comment: 6 journal pages, to appear in Physical Review

The Eskimo-Aleut Dentition: Crown and Root Morphology

Svrha rada: Rad daje pregled morfologije krune i korijena u populaciji Eskima Aleuta s američkog Arktika. U tom kontekstu uspoređuju se dentalne varijacije Eskima Aleuta s blisko povezanim američkim Indijancima i daljnje povezanim Europljanima. Materijali i metode: Karakterizacija varijacije učestalosti zubnih obilježja temelji se na opažanjima pokojnog Christyija G. Turnera II. i autora provedenima na približno 10 000 denticija. Šesnaest obilježja krune i pet obilježja korijena analizirano je prema smjernicama Dentoantropološkog sustava Državnoga sveučilišta u Arizoni. Rezultati: Od 21 razmatranog dentalnog obilježja samo su tri pokazala neznatne razlike između Eskima Aleuta, američkih Indijanaca i Europljana (peta kvržica na UM1, fisurni crtež na LM2, broj korijena na LM2). Za preostala je zabilježena drastična razlika između dviju populacija Novoga svijeta i Europljana. Iako općenito slični, Eskimi Aleuti i američki Indijanci razlikuju se u frekvencijama bilateralne meziopalatinalne rotacije (krilni Vpostav) na UI1, lopatastim i labijalno lopatastim sjekutićima, Carabellijevu svojstvu na UM1, tri kvržice na UM2, trokorijenskom UM2 i posebno trokorijenskom LM1. Zaključak: Razlike između triju skupina vjerojatno su rezultat genskoga odljeva i efekta osnivača, iako nedavno istraživanje alela EDAR V370A sugerira da neke dentalne varijable, poput lopatastog oblika i broja kvržica na donjim kutnjacima, mogu posredno odražavati prirodnu selekciju koja djeluje na druge varijable pod utjecajem toga alela.Objective of work: This paper provides an overview of crown and root morphology in Eskimo-Aleut populations of the American Arctic. For context, Eskimo-Aleut dental variation is compared to closely related American Indians and distantly related Europeans. Materials and methods: The characterization of dental trait frequency variation is based on observations made on approximately 10,000 dentitions scored by the late Christy G. Turner II and the author. Sixteen crown and five root traits were scored following the conventions outlined in the Arizona State University Dental Anthropology System. Results: Of the 21 dental traits considered, only three showed slight differences among Eskimo- Aleuts, American Indians, and Europeans (UM1 cusp 5, LM2 groove pattern, LM2 root number). For the remaining traits, there was typically a dramatic contrast between the two New World populations and Europeans. While generally similar, Eskimo-Aleuts and American Indians showed differences in UI1 winging, shoveling, and double shoveling, UM1 Carabelli trait, 2-cusped UM2, 3-rooted UM2, and especially 3-rooted LM1. Conclusion: The differences between the three groups are likely a product of genetic drift and founder effect although recent work on the EDAR V370A allele suggests some dental variables like shoveling and lower molar cusp number may indirectly reflect natural selection operating on other variables influenced by this allele

Vortical control of forced two-dimensional turbulence

A new numerical technique for the simulation of forced two-dimensional turbulence (Dritschel and Fontane, 2010) is used to examine the validity of Kraichnan-Batchelor scaling laws at higher Reynolds number than previously accessible with classical pseudo-spectral methods,making use of large simulation ensembles to allow a detailed consideration of the inverse cascade in a quasi-steady state. Our results support the recent finding of Scott (2007), namely that when a direct enstrophy cascading range is well-represented numerically, a steeper energy spectrum proportional to k^(−2) is obtained in place of the classical k^(−5/3) prediction. It is further shown that this steep spectrum is associated with a faster growth of energy at large scales, scaling like t^(−1) rather than Kraichnan’s prediction of t^(−3/2). The deviation from Kraichnan’s theory is related to the emergence of a population of vortices that dominate the distribution of energy across scales, and whose number density and vorticity distribution with respect to vortex area are related to the shape of the enstrophy spectrum. An analytical model is proposed which closely matches the numerical spectra between the large scales and the forcing scale

AFM imaging and plasmonic detection of organic thin-films deposited on nanoantenna arrays

In this study, atomic force microscopy (AFM) imaging has been used to reveal the preferential deposition of organic thin-films on patterned nanoantenna array surfaces - identifying the localised formation of both monolayer and multilayer films of octadecanethiol (ODT) molecules, depending on the concentration of the solutions used. Reliable identification of this selective deposition process has been demonstrated for the first time, to our knowledge. Organic thin-films, in particular films of ODT molecules, were deposited on plasmonic resonator surfaces through a chemi-sorption process - using different solution concentrations and immersion times. The nanoantennas based on gold asymmetric-split ring resonator (A-SRR) geometries were fabricated on zinc selenide (ZnSe) substrates using electron-beam lithography and the lift-off technique. Use of the plasmonic resonant-coupling technique has enabled the detection of ODT molecules deposited from a dilute, micromolar (1 M) solution concentration - with attomole sensitivity of deposited material per A-SRR – a value that is three orders of magnitude lower in concentration than previously reported. Additionally, on resonance, the amplitude of the molecular vibrational resonance peaks is typically an order of magnitude larger than that for the non-resonant coupling. Fourier-transform infrared (FTIR) spectroscopy shows molecule specific spectral responses – with magnitudes corresponding to the different film thicknesses deposited on the resonator surfaces. The experimental results are supported by numerical simulation

Deposition of Organic Molecules on Gold Nanoantennas for Sensing

The deposition of organic molecules on gold nanoantennas is reported through chemisorption for sensing in the midinfrared (mid-IR) spectral range. The specific nanostructures are gold asymmetric-split ring resonators (A-SRRs) based on circular-geometry with two different ‘arc’ lengths. The plasmonic resonant coupling technique was used to match the vibrational responses of the targeted molecules for their enhanced detection. Gold nanostructures are functionalised through chemisorption of octadecanethiol (ODT) in ethanol solution. The molecular vibrational responses were measured using a microscope coupled Fourier Transform Infrared (FTIR) spectroscopy. The experimental findings are closely supported using FDTD simulation. The modified nanoantennas surfaces are capable of supporting wide range of organic-sensing applications

Carman G. Blough: His personality and formative years

The article briefly explores the personality and psychological makeup of Carman G. Blough and discusses some experiences during his formative years that made Blough the person he was

AN ECONOMIC AND RISK ANALYSIS OF THE EFFECTS OF TILLAGE AND NITROGEN SOURCE ON SOIL CARBON SEQUESTRATION IN CORN PRODUCTION

The economic potential of no-tillage versus conventional tillage to sequester soil carbon using either commercial nitrogen or manure for continuous corn production is evaluated. Results indicate which system provides the highest net returns, which system is preferred by risk averse decision makers, and the price of carbon credits under alternative risk aversion preferences.Risk and Uncertainty,