Search results for "conical"
showing 10 items of 109 documents
Negative differential resistance and threshold-switching in conical nanopores with KF solutions
2021
Negative differential resistance (NDR) phenomena are under-explored in nanostructures operating in the liquid state. We characterize experimentally the NDR and threshold switching phenomena observed when conical nanopores are immersed in two identical KF solutions at low concentration. Sharp current drops in the nA range are obtained for applied voltages exceeding thresholds close to 1 V and a wide frequency window, which suggests that the threshold switching can be used to amplify small electrical perturbations because a small change in voltage typically results in a large change in current. While we have not given a detailed physical mechanism here, a phenomenological model is also includ…
A quantum dynamics study of the benzopyran ring opening guided by laser pulses
2014
Abstract The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of str…
Radiographic evaluation of conical tapered platform‐switched implants in the posterior mandible: 1‐year results of a two‐center prospective study
2015
Abstract Objective Long‐term success of dental implants depends on healthy peri‐implant soft tissues and adequate bone levels. This prospective study aims to assess bone level changes around implants with internal conical connection and platform‐switching abutments in the posterior mandible. Material and methods Adult patients missing at least two teeth in the posterior mandible and with a natural tooth mesial to the implant site received two or three adjacent internal conical connection implants. After a minimum transmucosal healing period of 8 weeks, single crown restorations were cemented over platform‐switching abutments. Changes in marginal bone levels were measured in standardized per…
Marginal soft tissue stability around conical abutments inserted with the one abutment-one time protocol after 5 years of prosthetic loading
2018
BACKGROUND Soft tissue stability is crucial to obtain and maintain optimal esthetic results. PURPOSE This study aimed to investigate, over 5 years, the soft tissue response using a conical abutment together with the "one-abutment one-time" (OA-OT) protocol in the restoration of implants inserted in the anterior esthetic area. MATERIAL AND METHODS From January 2011 to January 2012, all consecutive patients requiring an implant n the maxillary area between canines were enrolled. After submerged healing and osseointegration, a definitive abutment with a provisional crown was inserted. After 1 month, the definitive crown was delivered (Tdef). Analog impressions were taken before tooth extractio…
Clinical and radiographic performance of self‐locking conical connection implants in the posterior mandible: Five‐year results of a two‐centre prospe…
2021
Abstract Objective This prospective study aims to assess the 5‐year clinical performance of implants with internal conical connection and platform‐switched abutments in the posterior mandible. Material and Methods Healthy adults missing at least two teeth in the posterior mandible and with a natural tooth mesial to the implant site received two or three adjacent implants. After a transmucosal healing period single crown restorations were cemented on platform‐switched abutments. Changes in marginal bone levels were investigated in standardized periapical radiographs from surgery and loading (baseline) to 60‐months post‐loading. Results Twenty‐four patients received 52 implants. Bone remodell…
Pseudodifferential Analysis on Manifolds with Boundary — a Comparison of b-Calculus and Cone Algebra
2001
We establish a relation between two different approaches to a complete pseudodifferential analysis of totally characteristic or Fuchs type operators on compact manifolds with boundary respectively conical singularities: Melrose’s (overblown) b-calculus and Schulze’s cone algebra. Though quite different in their definition, we show that these two pseudodifferential calculi basically contain the same operators.
Charging a Capacitor from an External Fluctuating Potential using a Single Conical Nanopore
2015
We explore the electrical rectification of large amplitude fluctuating signals by an asymmetric nanostructure operating in aqueous solution. We show experimentally and theoretically that a load capacitor can be charged to voltages close to 1 V within a few minutes by converting zero time-average potentials of amplitudes in the range 0.5–3 V into average net currents using a single conical nanopore. This process suggests that significant energy conversion and storage from an electrically fluctuating environment is feasible with a nanoscale pore immersed in a liquid electrolyte solution, a system characteristic of bioelectronics interfaces, electrochemical cells, and nanoporous membranes.
Short hydrogen bonds enhance nonaromatic protein-related fluorescence
2021
Significance Intrinsic fluorescence of nonaromatic amino acids is a puzzling phenomenon with an enormous potential in biophotonic applications. The physical origins of this effect, however, remain elusive. Herein, we demonstrate how specific hydrogen bond networks can modulate fluorescence. We highlight the key role played by short hydrogen bonds, present in the protein structure, on the ensuing fluorescence. We provide detailed experimental and molecular evidence to explain these unusual nonaromatic optical properties. Our findings should benefit the design of novel optically active biomaterials for applications in biosensing and imaging.
On the relaxation mechanisms of 6-azauracil
2011
The nonadiabatic photochemistry of 6-azauracil has been studied by means of the CASPT2//CASSCF protocol and double-ζ plus polarization ANO basis sets. Minimum energy states, transition states, minimum energy paths, and surface intersections have been computed in order to obtain an accurate description of several potential energy hypersurfaces. It is concluded that, after absorption of ultraviolet radiation (248 nm), two main relaxation mechanisms may occur, via which the lowest (3)(ππ*) state can be populated. The first one takes place via a conical intersection involving the bright (1)(ππ*) and the lowest (1)(nπ*) states, ((1)ππ*/(1)nπ*)(CI), from which a low-energy singlet-triplet crossin…
Orbiting Orbitals: Visualization of Vi-Bronic Motion at a Conical Intersection
2013
The Jahn-Teller (JT) active unpaired electron of single metalloporphyrin radical anions is imaged through scanning tunneling microscopy. It is demonstrated that the electron is delocalized over the porphyrin macrocycle and its topographic image is determined by vibronic motion: the orbital of the electron adiabatically follows the zero-point pseudorotation of skeletal deformations. Transformation of the polar graphs of the observed images allows visualization of the adiabatic vibrational density to which the electron is coupled. The vibronic potential at the conical intersection is visualized and the half-integer angular momentum characteristic of the Berry phase is revealed in the radial f…