Critical properties of the metal-insulator transition in anisotropic systems

We study the three-dimensional Anderson model of localization with anisotropic hopping, i.e., weakly coupled chains and weakly coupled planes. In our extensive numerical study we identify and characterize the metal-insulator transition by means of the transfer-matrix method. The values of the critical disorder $W_c$ obtained are consistent with results of previous studies, including multifractal analysis of the wave functions and energy level statistics. $W_c$ decreases from its isotropic value with a power law as a function of anisotropy. Using high accuracy data for large system sizes we estimate the critical exponent as $\nu=1.62\pm0.07$. This is in agreement with its value in the isotropic case and in other models of the orthogonal universality class.Comment: 17 pages, 7 figures, requires svjour.csl and svepj.clo (included), submitted to EPJ

Stabilization of collapse and revival dynamics by a non-Markovian phonon bath

Semiconductor quantum dots (QDs) have been demonstrated to be versatile candidates to study the fundamentals of light-matter interaction [1-3]. In contrast with atom optics, dissipative processes are induced by the inherent coupling to the environment and are typically perceived as a major obstacle towards stable performances in experiments and applications [4]. In this paper we show that this is not necessarily the case. In fact, the memory of the environment can enhance coherent quantum optical effects. In particular, we demonstrate that the non-Markovian coupling to an incoherent phonon bath has a stabilizing effect on the coherent QD cavity-quantum electrodynamics (cQED) by inhibiting irregular oscillations and boosting regular collapse and revival patterns. For low photon numbers we predict QD dynamics that deviate dramatically from the well-known atomic Jaynes-Cummings model. Our proposal opens the way to a systematic and deliberate design of photon quantum effects via specifically engineered solid-state environments.Comment: 5 pages, 4 figure

Decision-making in Swiss home-like childbirth: A grounded theory study

Background: Decision-making in midwifery, including a claim for shared decision-making between midwives and women, is of major significance for the health of mother and child. Midwives have little information about how to share decision-making responsibilities with women, especially when complications arise during birth. Aim: To increase understanding of decision-making in complex home-like birth settings by exploring midwives’ and women’s perspectives and to develop a dynamic model integrating participatory processes for making shared decisions. Methods: The study, based on grounded theory methodology, analysed 20 interviews of midwives and 20 women who had experienced complications in home-like births. Findings: The central phenomenon that arose from the data was “defining/redefining decision as a joint commitment to healthy childbirth”. The sub-indicators that make up this phenomenon were safety, responsibility, mutual and personal commitments. These sub-indicators were also identified to influence temporal conditions of decision-making and to apply different strategies for shared decision-making. Women adopted strategies such as delegating a decision, making the midwife’s decision her own, challenging a decision or taking a decision driven by the dynamics of childbirth. Midwives employed strategies such as remaining indecisive, approving a woman’s decision, making an informed decision or taking the necessary decision. Discussion and conclusion: To respond to recommendations for shared responsibility for care, midwives need to strengthen their shared decision-making skills. The visual model of decision-making in childbirth derived from the data provides a framework for transferring clinical reasoning into practice

Stabilization of photon collapse and revival dynamics by a non-Markovian phonon bath

Solid state-based light emitters such as semiconductor quantum dots (QDs) have been demonstrated to be versatile candidates to study the fundamentals of light–matter interaction. In contrast to optics with isolated atomic systems, in the solid-state dissipative processes are induced by the inherent coupling to the environment and are typically perceived as a major obstacle toward stable performances in experiments and applications. In this theoretical model study we show that this is not necessarily the case. In fact, in certain parameter regimes, the memory of the solid-state environment can enhance coherent quantum optical effects. In particular, we demonstrate that the non-Markovian coupling to an incoherent phonon bath can exhibit a stabilizing effect on the coherent QD cavity-quantum electrodynamics by inhibiting irregular oscillations and allowing for regular collapse and revival patterns. For self-assembled GaAs/InAs QDs at low photon numbers we predict dynamics that deviate dramatically from the well-known atomic Jaynes–Cummings model. Even if the required sample parameters are not yet available in recent experimental achievements, we believe our proposal opens the way to a systematic and deliberate design of photon quantum effects via specifically engineered solid-state environments.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

GROWTH REGULATING FACTOR5 stimulates Arabidopsis chloroplast division, photosynthesis, and leaf longevity

Arabidopsis (Arabidopsis thaliana) leaf development relies on subsequent phases of cell proliferation and cell expansion. During the proliferation phase, chloroplasts need to divide extensively, and during the transition from cell proliferation to expansion, they differentiate into photosynthetically active chloroplasts, providing the plant with energy. The transcription factor GROWTH REGULATING FACTOR5 (GRF5) promotes the duration of the cell proliferation period during leaf development. Here, it is shown that GRF5 also stimulates chloroplast division, resulting in a higher chloroplast number per cell with a concomitant increase in chlorophyll levels in 35S: GRF5 leaves, which can sustain higher rates of photosynthesis. Moreover, 35S: GRF5 plants show delayed leaf senescence and are more tolerant for growth on nitrogen-depleted medium. Cytokinins also stimulate leaf growth in part by extending the cell proliferation phase, simultaneously delaying the onset of the cell expansion phase. In addition, cytokinins are known to be involved in chloroplast development, nitrogen signaling, and senescence. Evidence is provided that GRF5 and cytokinins synergistically enhance cell division and chlorophyll retention after dark-induced senescence, which suggests that they also cooperate to stimulate chloroplast division and nitrogen assimilation. Taken together with the increased leaf size, ectopic expression of GRF5 has great potential to improve plant productivity

Energy-level statistics at the metal-insulator transition in anisotropic systems

We study the three-dimensional Anderson model of localization with anisotropic hopping, i.e. weakly coupled chains and weakly coupled planes. In our extensive numerical study we identify and characterize the metal-insulator transition using energy-level statistics. The values of the critical disorder $W_c$ are consistent with results of previous studies, including the transfer-matrix method and multifractal analysis of the wave functions. $W_c$ decreases from its isotropic value with a power law as a function of anisotropy. Using high accuracy data for large system sizes we estimate the critical exponent $\nu=1.45\pm0.2$. This is in agreement with its value in the isotropic case and in other models of the orthogonal universality class. The critical level statistics which is independent of the system size at the transition changes from its isotropic form towards the Poisson statistics with increasing anisotropy.Comment: 22 pages, including 8 figures, revtex few typos corrected, added journal referenc

Multifractal analysis of the metal-insulator transition in anisotropic systems

We study the Anderson model of localization with anisotropic hopping in three dimensions for weakly coupled chains and weakly coupled planes. The eigenstates of the Hamiltonian, as computed by Lanczos diagonalization for systems of sizes up to $48^3$, show multifractal behavior at the metal-insulator transition even for strong anisotropy. The critical disorder strength $W_c$ determined from the system size dependence of the singularity spectra is in a reasonable agreement with a recent study using transfer matrix methods. But the respective spectrum at $W_c$ deviates from the ``characteristic spectrum'' determined for the isotropic system. This indicates a quantitative difference of the multifractal properties of states of the anisotropic as compared to the isotropic system. Further, we calculate the Kubo conductivity for given anisotropies by exact diagonalization. Already for small system sizes of only $12^3$ sites we observe a rapidly decreasing conductivity in the directions with reduced hopping if the coupling becomes weaker.Comment: 25 RevTeX pages with 10 PS-figures include

Giving birth : a hermeneutic study of the expectations and experiences of healthy primigravid women in Switzerland

Switzerland experiences one of the highest caesarean section rates in Europe but it is unclear why and when the decision is made to perform a caesarean section. Many studies have examined from a medical and physiological point of view, but research from a women's standpoint is lacking. Our aim was to develop a model of the emerging expectations of giving birth and the subsequent experiences of healthy primigravid women, across four cantons in Switzerland. This longitudinal study included 30 primigravidae from the German speaking, 14 from the French speaking and 14 from the Italian speaking cantons who were purposively selected. Data were collected by semi-structured interviews taking place around 22 and 36 weeks of pregnancy and six weeks and six months postnatally. Following Gadamer's hermeneutic, which in this study comprised 5 stages, a model was developed. Four major themes emerged: Decisions, Care, Influences and Emotions. Their meandering paths and evolution demonstrate the complexity of the expectations and experiences of women becoming mothers. In this study, women's narrated mode of birth expectations did not foretell how they gave birth and their lived experiences. A hermeneutic discontinuity arises at the 6 week postnatal interview mark. This temporary gap illustrates the bridge between women's expectations of birth and their actual lived experiences, highlighting the importance of informed consent, parent education and ensuring women have a positive birth and immediate postnatal experiences. Other factors than women's preferences should be considered to explain the increasing caesarean section rates

Giving birth: A hermeneutic study of the expectations and experiences of healthy primigravid women in Switzerland.

Switzerland experiences one of the highest caesarean section rates in Europe but it is unclear why and when the decision is made to perform a caesarean section. Many studies have examined from a medical and physiological point of view, but research from a women's standpoint is lacking. Our aim was to develop a model of the emerging expectations of giving birth and the subsequent experiences of healthy primigravid women, across four cantons in Switzerland. This longitudinal study included 30 primigravidae from the German speaking, 14 from the French speaking and 14 from the Italian speaking cantons who were purposively selected. Data were collected by semi-structured interviews taking place around 22 and 36 weeks of pregnancy and six weeks and six months postnatally. Following Gadamer's hermeneutic, which in this study comprised 5 stages, a model was developed. Four major themes emerged: Decisions, Care, Influences and Emotions. Their meandering paths and evolution demonstrate the complexity of the expectations and experiences of women becoming mothers. In this study, women's narrated mode of birth expectations did not foretell how they gave birth and their lived experiences. A hermeneutic discontinuity arises at the 6 week postnatal interview mark. This temporary gap illustrates the bridge between women's expectations of birth and their actual lived experiences, highlighting the importance of informed consent, parent education and ensuring women have a positive birth and immediate postnatal experiences. Other factors than women's preferences should be considered to explain the increasing caesarean section rates