824 research outputs found
An Intuitive Approach to Geometric Continuity for Parametric Curves and Surfaces (Extended Abstract)
The notion of geometric continuity is extended to an arbitrary order for curves and surfaces, and an intuitive development of constraints equations is presented that are necessary for it. The constraints result from a direct application of the univariate chain rule for curves, and the bivariate chain rule for surfaces. The constraints provide for the introduction of quantities known as shape parameters. The approach taken is important for several reasons: First, it generalizes geometric continuity to arbitrary order for both curves and surfaces. Second, it shows the fundamental connection between geometric continuity of curves and geometric continuity of surfaces. Third, due to the chain rule derivation, constraints of any order can be determined more easily than derivations based exclusively on geometric measures
Lasing from a circular Bragg nanocavity with an ultra-small modal volume
We demonstrate single-mode lasing at telecommunication wavelengths from a
circular nanocavity employing a radial Bragg reflector. Ultra-small modal
volume and Sub milliwatt pump threshold level are observed for lasers with
InGaAsP quantum well active membrane. The electromagnetic field is shown to be
tightly confined within the 300nm central pillar of the cavity. The quality
factors of the resonator modal fields are estimated to be on the order of a few
thousands.Comment: 3 pages, 4 figures Submitted to AP
Counterfactual reasoning and knowledge of possibilities
Williamson has argued against scepticism concerning our metaphysically modal knowledge, by arguing that standard patterns of suppositional reasoning to counterfactual conclusions provide reliable sources of correct ascriptions of possibility and necessity. The paper argues that, while Williamsonâs claims relating to necessity may well be right, he has not provided adequate reasons for thinking that the familiar modes of counterfactual reasoning to which he points generalise to provide a decent route to ascriptions of possibility. The paper also explores another path to ascriptions of possibility that may be extracted from Williamsonâs ideas, before briefly considering the general status of counterfactual reasoning in relation to our knowledge of possibilities
The Death Detectives
The death detectives is a series of blogs about death, photography and seeing the crime written in partnership with The Photographers' Gallery and Surviving Work
The open future, bivalence and assertion
It is highly intuitive that the future is open and the past is closedâwhereas it is unsettled whether there will be a fourth world war, it is settled that there was a first. Recently, it has become increasingly popular to claim that the intuitive openness of the future implies that contingent statements about the future, such as âthere will be a sea battle tomorrow,â are non-bivalent (neither true nor false). In this paper, we argue that the non-bivalence of future contingents is at odds with our pre-theoretic intuitions about the openness of the future. These are revealed by our pragmatic judgments concerning the correctness and incorrectness of assertions of future contingents. We argue that the pragmatic data together with a plausible account of assertion shows that in many cases we take future contingents to be true (or to be false), though we take the future to be open in relevant respects. It follows that appeals to intuition to support the non-bivalence of future contingents is untenable. Intuition favours bivalence
Stakes sensitivity and credit rating: a new challenge for regulators
The ethical practices of credit rating agencies (CRAs), particularly following the 2008 financial crisis, have been subject to extensive analysis by economists, ethicists, and policymakers. We raise a novel issue facing CRAs that has to do with a problem concerning the transmission of epistemic status of ratings from CRAs to the beneficiaries of the ratings (investors, etc.), and use it to provide a new challenge for regulators. Building on recent work in philosophy, we argue that since CRAs have different stakes than the beneficiaries of the ratings in the ratings being accurate, what counts as knowledge (and as having âepistemic statusâ) concerning credit risk for a CRA may not count as knowledge (as having epistemic status) for the beneficiary. Further, as it stands, many institutional investors (pension funds, insurance companies, etc.) are bound by law to make some of their investment decisions dependent on the ratings of officially recognized CRAs. We argue that the observation that the epistemic status of ratings does not transmit from CRAs to beneficiaries makes salient a new challenge for those who think current regulation regarding the CRAs is prudentially justified, namely, to show that the harm caused by acting on a rating that does not have epistemic status for beneficiaries is compensated by the benefit from them acting on a CRA rating that does have epistemic status for the CRA. Unlike most other commentators, therefore, we offer a defeasible reason to drop references to CRAs in prudential regulation of the financial industry
Evidence for Quantum Interference in SAMs of Arylethynylene Thiolates in Tunneling Junctions with Eutectic Ga-In (EGaIn) Top-Contacts
This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga2O3 as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J â 10-1 A/cm2 at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.
Molecular mechanisms for the regulation of histone mRNA stem-loop-binding protein by phosphorylation
As DNA is replicated during cell division, it must be packaged by histones. To match the level of available histones to DNA replication, histone mRNA expression is controlled by a 3âČ-end stem-loop structure unique to replication-dependent histone mRNAs. In Drosophila, this regulation is mediated by histone mRNA stem-loopâbinding protein (dSLBP), which has minimal tertiary structure when not bound to RNA. We show here that phosphorylation of dSLBP dramatically increases binding affinity for stem-loop RNA. The phosphorylated C-terminal tail of dSLBP does not contact RNA. Instead, increased negative charge on the C-terminal tail and stabilization of structural elements by a phosphorylation site within the RNA-binding domain promote more compact conformations that should reduce the entropic barrier to binding histone mRNA
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