Dependence of FRET efficiency on distance in single donor-acceptor pairs.

Possibility to create single donor-acceptor (D-A) pairs by attaching dye molecules to various sites of DNA strands with control of the inter-dye distance R enables one to measure average Förster resonance energy transfer (FRET) efficiency E as a function of R. Triplet states of the dyes influence the dependence E(R) considerably. Two types of FRET efficiency are considered: E = EA and E = ED. The efficiency EA(R) = JA(R)/[JA(R) + JD(R)] depends on the donor and the acceptor average intensities JD(R) and JA(R) measured in D- and A-fluorescence, whereas the efficiency ED(R) = 1 - JD(R)/JD(∞) depends only on the intensity of D-fluorescence, so-called the donor quenching method. The shape of the functions ED (R) and EA (R) depends strongly on whether the dyes have blinking fluorescence. FRET efficiencies ED (R) and EA (R) undergo the influence of many experimental factors and therefore, differ considerably from pure FRET efficiencies ED (s) (R) and EA (s) (R). Pure FRET efficiencies ED,A (s) (R) are calculated with the help of rate equations for D-A pairs, whose molecules have triplet states. It is shown how the calculated efficiencies ED,A (s) (R) can be compared to FRET efficiencies measured with the help of the intensities ID,A(R) corrected by cross talk and background light.

Two types of the relation between the intensity and the life time of photoluminescence of core/shell semiconductor quantum dots: important role of Coulomb field and tunneling transitions.

It has been recently found [Gh. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, and V. I. Klimov, Nature (London) 479, 203 (2011)] that semiconductor core/shell nanocrystals (NCs) with blinking photoluminescence (PL) can be of "A" or "B" type. NCs of A-type exhibit correlation between the intensity of PL and the life time. In NCs of B-type such correlation is absent. Simple model based on combination of the charging model and the two-level system model is proposed for describing emissive properties of NCs of both types. The model invokes fluctuations of emission ability γ(em) of NC to explain the emissive properties of NCs of B-type. Our combined model is also in agreement with anticorrelation between the duration τ(off) of off intervals and PL life time t(off) in off intervals found recently for NCs of A-type in the experiment [A. A. Cordones, T. J. Bixby, and S. R. Leone, Nano Lett. 11, 3366 (2011)].

Experimental demonstration of energy-chirp control in relativistic electron bunches using a corrugated pipe.

The first experimental study is presented of a corrugated wall device that uses wakefields to remove a linear energy correlation in a relativistic electron beam (a "dechirper"). Time-resolved measurements of both longitudinal and transverse wakefields of the device are presented and compared with simulations. This study demonstrates the feasibility to employ a dechirper for precise control of the beam phase space in the next generation of free-electron-lasers.

Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels.

The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy transfer rate F and for all four types of D-A pair. Comparison of the calculated D and A fluorescence trajectories with those measured by Weiss and co-workers proves the important role of triplet levels in energy transfer via singlet levels.

Photon statistics in blinking fluorescence of single PPV-PPyV molecule.

A theoretical six-level model for blinking fluorescence of single PPV-PPyV copolymer molecule excited by CW-laser light is proposed. The model has been chosen in accordance with the following facts found in the Paul Barbara group experiment: (i) alternation of two types of fluorescence with moderate and strong levels of emission, (ii) existence of "dark" states with no fluorescence, (iii) linear dependence of inverse on-interval duration on laser intensity, and (iv) existence of laser intensity independent off-intervals. Relations between the distribution function w''(N, T) for photons emitted by a single molecule, the distribution function w'(N, T) for photons arriving at photomultiplier tube (PMT) and photo-electric pulse distribution w(N, T) created in a PMT are discussed. The theory is able to describe pulse distribution function w(N, T) measured experimentally at signal acquisition time T = 0.1 s. Values of all rate constants of the model have been found from comparison of the theory with the experiment. Distributions w(on, off)(t) of on- and off-times and distribution w(N, T) of pulses have been calculated for infrequent and frequent inter-conformational jumps in single copolymer molecule.

A unit-coordinator system: an effective method of reducing inappropriate hospital stays.

BACKGROUND: Many hospitals would benefit from a reduction in the length of inpatient hospital stays; in this regard, nursing approaches require complementation to ensure optimized nursing care. Such action is particularly important in general hospitals in Korea, where the ratio of patients to nurses is more than 10:1. OBJECTIVES: This study aimed to determine the effectiveness of a unit-coordinator system in complementing primary nursing in general hospitals as a means of reducing inappropriate hospital stays. METHODS: The unit-coordinator system was implemented in seven wards in a hospital in Seoul for 8 weeks. The existing primary nursing system was maintained, and newly placed unit-coordinators organized the activities within each ward. The numbers of early admissions and early discharges were determined by assessing the electronic administrative records of the hospital. Further, the number of patients who had undergone check-ups and chemotherapy on the day of admission was confirmed from the daily reports of each ward. The effect of the unit-coordinator system on nurse satisfaction was assessed through direct interviews. FINDINGS: Early-discharge and early-admission numbers increased significantly after implementation of the unit-coordinator system. Early admission allowed check-ups and treatments to be performed on the day of admission. Thus, this system reduced the length of hospital stay by 1 day, and the total reduction of inappropriate hospital stays over the 8-week study period was 66 days. Further, the unit-coordinator system also increased nurse satisfaction. CONCLUSION: The unit-coordinator system is an effective method of complementing primary nursing and reducing inappropriate hospital stays.

Family planning practice and related factors of married women in Ethiopia.

BACKGROUND: The family planning (FP) practice rate of Ethiopian women of reproductive age is lower than in most other sub-Saharan African countries. AIM: To examine the status of FP practice and identify intrapersonal, interpersonal and community factors associated with FP practice among married Ethiopian women in a rural area. METHODS: A cross-sectional survey was conducted with a convenient sample of 193 married women of reproductive age. A structured questionnaire, which was modified based on the Ethiopian Demographic Health Survey, was used. Multiple logistic regression analysis was conducted to identify factors associated with FP practice at three levels: intrapersonal, interpersonal and community. RESULTS: Almost 67% of women were currently using at least one FP method and most women obtained FP methods from the public health sector. Short-term methods such as pills and injections were most commonly used. FP practice was significantly associated with willingness to use long-term or permanent FP methods in future and spousal discussion about FP. CONCLUSIONS: Both intrapersonal and interpersonal factors were related to FP practice. Community factors, however, need to be further assessed using various methods to plan a comprehensive and more culturally acceptable community-based FP program. Caution is needed to generalize the findings because of the convenient sample, but community-based FP programs emphasizing long-term or permanent methods and male involvement in FP counseling would be successful strategies to increase FP practice. IMPLICATIONS FOR NURSING PRACTICE: Nurses and midwives need to be trained to provide knowledge and skills for long-term or permanent FP methods for service quality.

Super-Poissonian statistics of on-off jumps in blinking fluorescence of single molecules.

Blinking fluorescence of a single guest molecule embedded in a polymer matrix and excited by cw laser light is considered. Such fluorescence exhibits quantum jumps from bright on-intervals to dark off-intervals, i.e., so-called on-->off jumps. A system with one type of on-intervals and with two types of off-intervals is studied. A distribution function w(N)(T) for the number N of on-->off jumps in a time interval T is derived. The distribution function is expressed via a threefold integral of three Poissonian functions, each of which relates to the corresponding exponential process in the quantum dynamics of a fluorescent impurity center. Numerical calculations of the distribution function w(N)(T) for four time intervals T of various durations are carried out. The distribution function w(N)(T) is broader as compared with the Poissonian one and has two maxima, one of which relates to observed time intervals without on-->off jumps.

[Construction of secalotriticum (rye-wheat amphidiploids with the rye cytoplasm (RRAABB, 2n = 42)), the formation of the karyotypes of the F1BC1 and F1BC2 rye-triticale amphidiploids, and commercial and biological characteristics of the early secalotriticum generations].

The karyotype formation was studied in the F1BC1 and F1BC2 hybrids of Secale cereale L. ssp. tetraplodium Kobyl. (RRRR, 4x = 28) and Triticale (AABBRR, 6x = 42). The hybrid karyotypes were heterogenomic for homeologous chromosome groups of the wheat and rye genomes. The hybrids differed in cytological stability, the balance of chromosomes of the original species, and the fertility of spikes. The majority of F1BC1 and F1BC2 plants were cytologically unstable and unbalanced in chromosome composition and displayed a low spike fertility. Cytologically stable hexaploids occurred in F1BC1 and F1BC2 at a frequency of 1.0 and 9.5%, respectively. The resulting hexaploid secalotriticum lines (RRAABB, 6x = 42) were genotypically diverse and morphogenetically various. The genetic factors responsible for the diversity of the F1BC1 and F1BC2 rye-triticale amphiploids and early secalotriticum generations are discussed.

Manifestation of single macromolecule quantum dynamics in photon distribution function of blinking fluorescence.

Distribution function w(N)(T) for photons created by three-level nanoparticle in time interval T under cw laser excitation is calculated for various methods of photon counting. It is found that each exponential process exp(-lambda(i)t) in quantum dynamics of three-level nanoparticle manifests itself via Poissonian function P(N)(lambda(i)t)=(lambda(i)t)(N) exp(-lambda(i)t)/N! in the photon distribution function w(N)(T). The distribution function w(N)(T) is expressed via two or three integrals of two or three Poissonian functions P(N)(lambda(i)t). The simple mathematical expression for w(N)(T) enables one to calculate photon distribution in blinking fluorescence with on and off intervals. A scaling between photon distribution function w(N)(T) and photoelectric pulse distribution function w(n)(T) is found. Comparison of the theoretical distribution w(n)(T) and the distribution measured in blinking fluorescence of single polymer molecule dPPV-PPyV and complex organic molecule 1,1(')-didodecyl-3,3,3('),3(')-tetramethylindocarbocyanine perchlorate (DiI) is carried out. The theoretical distributions are able to describe those found in an experiment.

Theoretical treatment of scan time dependent optical bands of single molecule embedded in polymer or glass.

A theoretical framework for the description of fluctuating absorption coefficients of a guest molecule embedded in polymer or glass is presented. These fluctuations emerge in experiments with scans of laser frequency. A relation between theoretical expression for the time dependent single molecule absorption coefficient and the absorption coefficient measured in experiments with scanning laser frequency is discussed. The analysis is carried out for a guest molecule whose optical band consists of two well-resolved and poorly resolved optical lines. For well-resolved optical lines, measurement of auto- and cross-correlators is proposed. These correlators enable one to compare the fluctuating absorption coefficient with the time dependent absorption coefficient calculated theoretically with no adjustable parameters. For poorly resolved optical lines, the time dependent absorption coefficient enables one to calculate temporal line broadening of single molecule and to compare it with measured line broadening in time scale of seconds.

Quasimonoenergetic electron beam generation by using a pinholelike collimator in a self-modulated laser wakefield acceleration.

A relativistic electron bunch with a large charge (>2 nC) was produced from a self-modulated laser wakefield acceleration configuration. For this experiment, an intense laser beam with a peak power of 2 TW and a duration of 700 fs was focused in a supersonic He gas jet, and relativistic high-energy electrons were observed from the strong laser-plasma interaction. By passing the electron bunch through a small pinholelike collimator, we could generate a quasimonoenergetic high-energy electron beam, in which electrons within a cone angle of 0.25 mrad (f/70) were selected. The beam clearly showed a narrow-energy-spread behavior with a central energy of 4.3 MeV and a charge of 200 pC. The acceleration gradient was estimated to be about 30 GeV/m. Particle-in-cell simulations were performed for comparison study and the result shows that both the experimental and simulation results are in good agreement and the electron trapping is initiated by the slow beat wave of the Raman backward wave and the incident laser pulse.

[Construction of rye-wheat amphidiploids with the cytoplasm of rye-secalotriticum (RRAABB, 2n = 42): meiosis characteristics in rye-triticale F1 hybrids (RRABR, 5x = 35)].

Results of cytogenetic analysis of microsporogenesis in rye-triticale F1 hybrids (RRABR, 5x = 35) are presented. Meiosis of pentaploids is described as the key stage in the synthesis of secalotriticum, lines with intergenomic substitutions of chromosomes, or alloplasmic rye and wheat lines. Properties of meiotic processes and cytological mechanisms in formation of functional gametes and plants of various genomic and chromosomal composition are discussed.

Factors influencing long-term home care utilization by the older population: implications for targeting.

This research was designed to explore factors that affect the choice of long-term care modalities in the older population and to discuss the appropriate target population of home health care services within the entire long-term care system. The study subjects' activities of daily living limitations, cognitive status, and sociodemograhic data at the time of admission were obtained from retrospective chart reviews. The sample included 134 older subjects who were receiving long-term care from a Long-Term Home Health Care Program or a nursing home in New York City. The results indicated that Long-Term Home Health Care Program use by older persons was characterized by a higher rate of being admitted from private homes, less cognitive impairments, less limitations in activities of daily living, and younger age than older patients who were nursing home residents. Consequently, in the choice of different care modalities, health-related factors of the older population were found to be more important predictors than sociodemographic characteristics or support system. The implication to both nurses and researchers is the development of eligibility criteria that captures the unique characteristics of disabled older persons in each of the different long-term care programs to serve them better in a cost-effective manner.

Spatio-temporal measurement of beam properties in the PLS diagnostic beamline.

A diagnostic beamline is being constructed in the PLS storage ring for measurement of electron- and photon-beam properties. It consists of two 1:1 imaging systems: a visible-light imaging system and a soft X-ray imaging system. In the visible-light imaging system, the transverse beam size and beam position are measured with various detectors: a CCD camera, two photodiode arrays and a photon-beam position monitor. Longitudinal bunch structure is also investigated with a fast photodiode detector and a picosecond streak camera. On the other hand, the soft X-ray imaging system is under construction to measure beam sizes with negligible diffraction-limited error. The X-ray image optics consist of a flat cooled mirror and two spherical focusing mirrors.