Nonexponential statistics of fluorescence photobleaching

In this paper, I consider theoretical models of the decay via photobleaching of a sample of surface-immobilized fluorescent molecules excited by a spatially varying laser intensity profile. I show that, with mild restrictions on the photobleaching mechanism, the fluorescence decay measured in a nonuniform excitation profile is always nonexponential. Under the same conditions, the fluorescence decay can always be approximated by a discrete sum of exponentials. A particular example is given in which a homogeneous population of fluorophores with a single (intensity-dependent) photobleaching lifetime, when illuminated by a Gaussian laser, exhibits power law fluorescence decay at long times. These results indicate that the observation of multiple exponentials in single molecule or ensemble photobleaching lifetime measurements can arise solely as an artifact of a spatially varying laser profile and is not necessarily indicative of heterogeneity in molecular internal states, conformation, or local environment

Photon statistics and dynamics of Fluorescence Resonance Energy Transfer

We report high time-resolution measurements of photon statistics from pairs of dye molecules coupled by fluorescence resonance energy transfer (FRET). In addition to quantum-optical photon antibunching, we observe photon bunching on a timescale of several nanoseconds. We show by numerical simulation that configuration fluctuations in the coupled fluorophore system could account for minor deviations of our data from predictions of basic Forster theory. With further characterization we believe that FRET photon statistics could provide a unique tool for studying DNA mechanics on timescales from 10^-9 to 10^-3 s.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Tracking-FCS: Fluorescence correlation spectroscopy of individual particles

We exploit recent advances in single-particle tracking to perform fluorescence correlation spectroscopy on individual fluorescent particles, in contrast to traditional methods that build up statistics over a sequence of many measurements. By rapidly scanning the focus of an excitation laser in a circular pattern, demodulating the measured fluorescence, and feeding these results back to a piezoelectric translation stage, we track the Brownian motion of fluorescent polymer microspheres in aqueous solution in the plane transverse to the laser axis. We discuss the estimation of particle diffusion statistics from closed-loop position measurements, and we present a generalized theory of fluorescence correlation spectroscopy for the case that the motion of a single fluorescent particle is actively tracked by a time-dependent laser intensity. We model the motion of a tracked particle using Ornstein-Uhlenbeck statistics, using a general theory that contains a umber of existing results as specific cases. We find good agreement between our theory and experimental results, and discuss possible future applications of these techniques to passive, single-shot, single-molecule fluorescence measurements with many orders of magnitude in time resolution

Feedback localization of freely diffusing fluorescent particles near the optical shot-noise limit

We report near-optimal tracking of freely diffusing fluorescent particles in a quasi-two-dimensional geometry via photon counting and real-time feedback. We present a quantitative statistical model of our feedback network and find excellent agreement with the experiment. We monitor the motion of a single fluorescent particle with a sensitivity of 15 nm/sqrt Hz while collecting fewer than 5000 fluorescence photons/s. Fluorescent microspheres (diffusion coefficient 1.3 μm^2/s) are tracked with a root-mean-square tracking error of 170 nm, within a factor of 2 of the theoretical limit set by photon counting shot noise

Landscape Character Assessment as an Approach to Understanding Public Interests within the European Landscape Convention

The European Landscape Convention’s (ELC) definition of landscape, ‘‘an area, as perceived by people. . .’’, places the public central to any understanding of landscape. This paper argues for ‘just’ involvement of the public and looks at how the focus of landscape as a perceived entity has been taken up within Landscape Character Assessment (LCA), an approach applied in England and Scotland for implementing the ELC. Based on a conceptual framework grounded in perception as a phenomenological experience of landscape and informed by principles of participation, LCAs from 2007 to 2011 have been assessed as to how public involvement has been considered. The results show that only a quarter of all assessments accessed involved the public, and that among these there is great disparity in the degree to which the public is engaged

Expand+Functional selection and systematic analysis of intronic splicing elements identify active sequence motifs and associated splicing factors

Despite the critical role of pre-mRNA splicing in generating proteomic diversity and regulating gene expression, the sequence composition and function of intronic splicing regulatory elements (ISREs) have not been well elucidated. Here, we employed a high-throughput in vivo Screening PLatform for Intronic Control Elements (SPLICE) to identify 125 unique ISRE sequences from a random nucleotide library in human cells. Bioinformatic analyses reveal consensus motifs that resemble splicing regulatory elements and binding sites for characterized splicing factors and that are enriched in the introns of naturally occurring spliced genes, supporting their biological relevance. In vivo characterization, including an RNAi silencing study, demonstrate that ISRE sequences can exhibit combinatorial regulatory activity and that multiple trans-acting factors are involved in the regulatory effect of a single ISRE. Our work provides an initial examination into the sequence characteristics and function of ISREs, providing an important contribution to the splicing code

Resident physicians’ perceptions of ambulatory care pharmacy

Background: Physicians\u27 acceptance of clinical pharmacy services is dependent on exposure to those services, with use increasing as resident physicians progress through their training. Resident physicians train within environments that have a multidisciplinary teaching and clinical care approach, working closely with other healthcare professionals. Ambulatory care pharmacists are increasingly working with resident physicians in clinic settings as part of the multidisciplinary team, and identification of resident physicians’ perceptions may influence future collaboration. Objective: The objective of this research is to evaluate the perception of ambulatory care clinical pharmacy services from the perspective of resident physicians. Methods: A statewide network of ambulatory care pharmacists was identified and received an electronic questionnaire. Pharmacists working within clinics that serve as training sites for resident physicians then completed and distributed questionnaires to the resident physicians within their clinical site. Items related to demographics and perception of involvement and interactions with clinical pharmacists. Results: Forty-five resident physicians responded from four unique clinical sites (response rate = 42%). They agreed or strongly agreed that pharmacists help patients obtain their therapeutic goals (97.8%), are able to educate patients effectively (95.6%), provide high quality care (97.8%), and do a good job helping co-manage patients (91.1%). Previous exposure to pharmacists was limited primarily to the drugstore (48.9%) and hospital (51.1%) settings. Resident physicians in the third year of training and those reporting a friend was a pharmacist, were more likely to have a positive perception of the pharmacist’s role as a resident educator (p=0.048 and p=0.044, respectively). Conclusions: Resident physicians with a longer duration of exposure and personal friendship with a pharmacist are more likely to express positive perceptions. Areas for further enhancements in this interprofessional relationship related to perceptions about pharmacist autonomy and patient relationships were identified

Triple Interference, Non-linear Talbot Effect and Gravitization of the Quantum

Recently we have discussed a new approach to the problem of quantum gravity in which the quantum mechanical structures that are traditionally fixed, such as the Fubini-Study metric in the Hilbert space of states, become dynamical and so implement the idea of gravitizing the quantum. In this paper we elaborate on a specific test of this new approach to quantum gravity using triple interference in a varying gravitational field. Our discussion is driven by a profound analogy with recent triple-path interference experiments performed in the context of non-linear optics. We emphasize that the triple interference experiment in a varying gravitational field would deeply influence the present understanding of the kinematics of quantum gravity and quantum gravity phenomenology. We also discuss the non-linear Talbot effect as another striking phenomenological probe of gravitization of the geometry of quantum theory.Comment: 27 pages, 2 figures. arXiv admin note: text overlap with arXiv:2203.1713