bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the quantum physical relation between photon tunnelling and near‐field optics
Authors: Keller O. 
Published: March 2003

The standard theory of optical tunnelling based on a mathematical analogy between the time‐independent one‐particle Schrödinger equation describing electron tunnelling and the Helmholtz equation for the macroscopic electric field is criticized. In a classical perspective photons are related to the dynamics of the transverse part of the electromagnetic field, and with the assumption that the electrons in a coupled photon‐atom system are driven in a linear fashion by the field, a rigorous integro‐differential equation for the transverse field is established. In the near‐field zone of matter a transverse self‐field exists and this may cause the appearance of superluminality in optical tunnelling. In the wake of a brief review of the space‐time dynamics of free photons, a first‐quantized description of the birth process of a single polychromatic photon in the near‐field region of an active atom (molecule, mesoscopic particle) is presented, and afterwards the link between photon localizability, Einstein causality and near‐field photon tunnelling is discussed. On the basis of a new one‐photon quantum theory of near‐field scattering from a microscopic (or mesoscopic) object, it is shown that photon tunnelling always appears in photon‐atom scattering. A first‐order Born approximation cannot capture the phenomenon, however. The emergence of the energy wave function of the scattered photon is followed in space and time.
Misorientation distributions in hot deformed NaCl using electron backscattered diffraction
Authors: Pennock G. M. , Drury M. R. , Trimby P. W. , Spiers C. J. 
Published: March 2003

SummaryEBSD orientation mapping has been used to derive subgrain boundary misorientation distributions in a series of hot deformed and etched NaCl samples. The main objective of this study has been to examine the influence of data processing, noise caused by angular resolution limits and step size on the subgrain misorientation distributions in hot deformed NaCl. Processing of non‐indexed EBSD patterns increased the average misorientations in etched NaCl. Noise contributed significantly to low angle misorientation peaks for step sizes less than the minimum subgrain size. Orientation data collected using a step size larger than the average subgrain size cumulated misorientations across individual subgrains and effectively measured an orientation gradient between steps. Orientation gradient distributions were not influenced by noise. Average misorientation values calculated from large step data correlated well with average misorientation from small step size data. Average misorientations showed a power law relationship with strain. Three types of substructures were identified using scanning electron microscopy and EBSD mapping, equiaxed subgrains, long subgrain boundaries and a core‐mantle subgrain arrangement.
Quantitative phase‐amplitude microscopy I: optical microscopy
Authors: Barone‐Nugent E. D. , Barty A. , Nugent K. A. 
Published: March 2003

SummaryIn this paper, the application of a new optical microscopy method (quantitative phase‐amplitude microscopy) to biological imaging is explored, and the issue of resolution and image quality is examined. The paper begins by presenting a theoretical analysis of the method using the optical transfer function formalism of Streibl (1985). The effect of coherence on the formation of the phase image is explored, and it is shown that the resolution of the method is not compromised over that of a conventional bright‐field image. It is shown that the signal‐to‐noise ratio of the phase recovery, however, does depend on the degree of coherence in the illumination. Streibl (1985) notes that partially coherent image formation is a non‐linear process because of the intermingling of amplitude and phase information. The work presented here shows that the quantitative phase‐amplitude microscopy method acts to linearize the image formation process, and that the phase and amplitude information is properly described using a transfer function analysis. The theoretical conclusions are tested experimentally using an optical microscope and the theoretical deductions are confirmed.Samples for microscopy influence both the phase and amplitude of the light wave and it is demonstrated that the new phase recovery method can separate the amplitude and phase information, something not possible using traditional phase microscopy. In the case of a coherent wave, knowledge of the phase and amplitude constitutes complete information that can be used to emulate other forms of microscopy. This capacity is demonstrated by recovering the phase of a sample and using the data to emulate a differential interference contrast image.
Direct modulation of the effective sensitivity of a CCD detector: a new approach to time‐resolved fluorescence imaging
Authors: Mitchell A. C. , Wall J. E. , Murray J. G. , Morgan C. G. 
Published: March 2003

SummaryIn this paper a novel approach to frequency‐domain fluorescence lifetime imaging (FLIM) is described. In a CCD camera a single pixel is defined by a charge pattern on a group of electrodes. By modulation of the pattern of voltages defining the pixel structure it is possible to modulate the sensitivity of the CCD at radio frequency. The modulation enhances the noise performance of the CCD, in contrast to the deterioration in performance seen when an intensifier stage is similarly modulated. The new technology has potential applications to a wide range of assays as well as in conventional FLIM applications. Unlike intensifier‐based systems, the directly modulated CCD is physically small, inexpensive, robust and offers superior resolution and noise performance.
Measurement of magnetic domain wall width using energy‐filtered Fresnel images
Authors: Lloyd S. J. , Loudon J. C. , Midgley P. A. 
Published: March 2003

SummaryMagnetic domain walls in Nd2Fe14B have been examined using a series of energy‐filtered Fresnel images in the field emission gun transmission electron microscope (FEGTEM). We describe the changes in the intensity distribution of the convergent wall image as a function of defocus, foil thickness and domain wall width. The effect of tilted domain walls and beam convergence on the fringe pattern is also discussed. A comparison of the experimental intensity profile with that from simulations allows the domain wall width to be determined. Measurement of very narrow walls is made possible only by using a relatively thick foil, which necessitates energy‐filtering to allow quantitative comparison with simulations. The magnetic domain wall width in Nd2Fe14B was found to be 3 ± 2 nm.
Fluorescence resonance energy transfer from cyan to yellow fluorescent protein detected by acceptor photobleaching using confocal microscopy and a single laser
Authors: Karpova T. S. , Baumann C. T. , He L. , Wu X. , Grammer A. , Lipsky P. , Hager G. L. , McNally J. G. 
Published: March 2003

SummaryOne manifestation of fluorescence resonance energy transfer (FRET) is an increase in donor fluorescence after photobleaching the acceptor. Published acceptor‐photobleaching methods for FRET have mainly used wide‐field microscopy. A laser scanning confocal microscope enables faster and targeted bleaching within the field of view, thereby improving speed and accuracy. Here we demonstrate the approach with CFP and YFP, the most versatile fluorescent markers now available for FRET. CFP/YFP FRET imaging has been accomplished with a single laser (argon) available on virtually all laser‐scanning confocal microscopes. Accordingly, we also describe the conditions that we developed for dual imaging of CFP and YFP with the 458 and 514 argon lines. We detect FRET in a CFP/YFP fusion and also between signalling molecules (TNF‐Receptor‐Associated‐Factors or TRAFs) that are known to homo‐ and heterotrimerize. Importantly, we demonstrate that appropriate controls are essential to avoid false positives in FRET by acceptor photobleaching. We use two types of negative control: (a) an internal negative control (non‐bleached areas of the cell) and (b) cells with donor in the absence of the acceptor (CFP only). We find that both types of negative control can yield false FRET. Given this false FRET background, we describe a method for distinguishing true positive signals. In summary, we extensively characterize a simple approach to FRET that should be adaptable to most laser‐scanning confocal microscopes, and demonstrate its feasibility for detecting FRET between several CFP/YFP partners.
Effects of Chronic Oestrogen Replacement on Stress‐Induced Activation of Hypothalamic‐Pituitary‐Adrenal Axis Control Pathways
Authors: Dayas C. V. , Xu Y. , Buller K. M. , Day T. A. 
Published: March 2003

AbstractOestrogen replacement therapy reportedly suppresses hypothalamic‐pituitary‐adrenal (HPA) axis responses to an emotional stressor in postmenopausal women. However, most studies in the rat suggest a facilitatory role for oestrogen in the control of HPA axis function. One explanation for this difference may be the regimen of oestrogen replacement: during oestrogen replacement therapy, oestrogen levels are low and constant whereas most animal studies examined the HPA axis response when oestrogen levels are rising. In the present study, we assessed HPA axis stress responses in mature ovariectomized rats after plasma oestrogen levels had been maintained at physiological levels for a prolonged period (25 or 100 pg/ml for 7 days). In the case of both an emotional stressor (noise) and a physical stressor (immune challenge by systemic interleukin‐1β administration), oestrogen replacement suppressed stress‐related Fos‐like immunolabelling, in hypothalamic neuroendocrine cells and plasma adrenocorticotropin hormone responses. From the present data, and past reports, it appears unlikely that these effects of oestrogen are due to a direct action on corticotropin‐releasing factor or oxytocin cells. Therefore, to obtain some indication of oestrogen's possible site(s) of action, Fos‐like immunolabelling was mapped in the amygdala and in brainstem catecholamine groups, which are neuronal populations demonstrating substantial evidence of involvement in the generation of HPA axis stress responses. In the amygdala, oestrogen replacement suppressed central nucleus responses to immune challenge, but not to noise. Amongst catecholamine cells, oestrogen replacement was more effective against responses to noise than immune challenge, suppressing A1 and A2 (noradrenergic) and C2 (adrenergic) responses to noise, but only A1 responses to immune challenge. These data suggest that, as in postmenopausal women on oestrogen replacement therapy, chronic low‐level oestrogen replacement can suppress HPA axis stress responses in the rat. Moreover, oestrogen appears to exert effects at multiple sites within putative HPA axis control pathways, even though most of the relevant neuronal populations do not contain genomic receptors for this gonadal steroid and the pattern of oestrogen action differs for an emotional vs a physical stressor.
Thyroid Hormones Regulate Pituitary Growth Hormone Secretagogue Receptor Gene Expression
Authors: Kamegai J. , Tamura H. , Ishii S. , Sugihara H. , Wakabayashi I. 
Published: March 2003

AbstractThyroid hormones regulate growth hormone (GH) secretion by actions both at the hypothalamus and at the pituitary gland. At the level of the pituitary, thyroid hormones increase GH and GH‐releasing hormone receptor (GHRH‐R) mRNA expression. To test if thyroid hormones might also regulate the pituitary expression of mRNA for the recently identified GH secretagogue (GHS) receptor, GHS‐R, primary pituitary cell cultures from adult male rats were treated with triiodothyronine (T3) and GHS‐R mRNA levels were assessed by reverse transcriptase‐polymerase chain reaction. T3 increased pituitary GHS‐R mRNA levels in a dose‐ and time‐dependent manner. The stimulatory action of T3 on GHS‐R mRNA levels was also observed in the presence of the RNA synthesis inhibitor, actinomycin D, indicating that gene transcription is not required. Closer examination of the decay rates of GHS‐R mRNA in the presence of actinomycin D revealed T3 extended the half‐life of the GHS‐R mRNA from 8 h (basal) to15 h, demonstrating that T3 increases GHS‐R mRNA levels in vitro by increasing message stability.
Oestradiol Microimplants in the Ventromedial Preoptic Area Inhibit Secretion of Luteinizing Hormone via Dopamine Neurones in Anoestrous Ewes
Authors: Anderson G. M. , Connors J. M. , Hardy S. L. , Valent M. , Goodman R. L. 
Published: March 2003

AbstractOestradiol exerts a season‐specific negative feedback effect on the GnRH/LH neurosecretory system of the Suffolk ewe. This neuroendocrine suppression is mediated in part by dopamine A15 neurones, but these neurones do not possess the oestrogen receptor. Based on indirect evidence, we hypothesized that oestrogen receptor‐containing neurones in the ventromedial preoptic area (vmPOA) may be the initial step in a neuronal system whereby oestradiol suppresses GnRH secretion during the non‐breeding season. To test this, three experiments were conducted using ovariectomized ewes receiving either empty or oestradiol‐containing bilateral microimplants directed at the vmPOA or s.c. subcutaneous oestradiol‐containing implants. In the first experiment, LH pulse frequency was measured on days 0, 1, 7 and 14 of treatment during seasonal anoestrus. In vmPOA oestradiol and s.c. oestradiol groups only, LH pulse frequency was suppressed on days 7 and 14, with maximal suppression evident by day 7. In the second experiment, this protocol was repeated during the breeding season, with LH pulses examined on days 0 and 7; LH pulse frequency did not change in any group. The third experiment tested if the effect of vmPOA oestradiol during anoestrus could be overcome by an injection of the dopamine‐D2 receptor antagonist (–)‐sulpiride. The vmPOA microimplants and s.c. oestradiol implants again suppressed LH pulse frequency and this was reversed by sulpiride in vmPOA oestradiol ewes. We conclude that oestradiol acts on cells in the vmPOA to stimulate a system involving dopamine neurones that inhibits GnRH/LH pulsatility in the anoestrous ewe.
Functional Cross‐Talk Between the Hypothalamic‐Pituitary‐Gonadal and ‐Adrenal Axes
Authors: Viau V. 
Published: March 2003

AbstractUnder normal conditions, the adrenal glucocorticoids, the endproduct of the hypothalamic‐pituitary‐adrenal (HPA) axis, provide a frontline of defence against threats to homeostasis (i.e. stress). On the other hand, chronic HPA drive and glucocorticoid hypersecretion have been implicated in the pathogenesis of several forms of systemic, neurodegenerative and affective disorders. The HPA axis is subject to gonadal influence, indicated by sex differences in basal and stress HPA function and neuropathologies associated with HPA dysfunction. Functional cross‐talk between the gonadal and adrenal axes is due in large part to the interactive effects of sex steroids and glucocorticoids, explaining perhaps why several disease states linked to stress are sex‐dependent. Realizing the interactive nature by which the hypothalamic‐pituitary‐gonadal and HPA systems operate, however, has made it difficult to model how these hormones act in the brain. Manipulation of one endocrine system is not without effects on the other. Simultaneous manipulation and assessment of both endocrine systems can overcome this problem. This dual approach in the male rat reveals that testosterone can act and interact on different aspects of basal and stress HPA function. Basal adrenocorticotropic hormone (ACTH) release is regulated by testosterone‐dependent effects on arginine vasopressin synthesis, and corticosterone‐dependent effects on corticotropin‐releasing hormone (CRH) synthesis in the paraventricular nucleus (PVN) of the hypothalamus. In contrast, testosterone and corticosterone interact on stress‐induced ACTH release and drive to the PVN motor neurones. Candidate structures mediating this interaction include several testosterone‐sensitive afferents to the HPA axis, including the medial preoptic area, central and medial amygdala and bed nuclei of the stria terminalis. All of these relay homeostatic information and integrate reproductive and social behaviour. Because these modalities are affected by stress in humans, a dual systems approach holds great promise in establishing further links between the neuroendocrinology of stress and the central bases of sex‐dependent disorders, including psychiatric, cardiovascular and metabolic disease.
Comparison Between the Influence of the Intravenous and Intracerebroventricular Injection of a Nitric Oxide Donor on Adrenocorticotropic Hormone Release and Hypothalamic Neuronal Activity
Authors: Seo D. O. , Lee S. , Rivier C. 
Published: March 2003

AbstractWe investigated the ability of the nitric oxide (NO) donor 3‐morpholino‐sydnonimine (SIN‐1) to release adrenocorticotropic hormone (ACTH) and up‐regulate hypothalamic neurones following its intravenous (i.v.) injection. i.v. SIN‐1 (0.2–1.8 mg/kg) produced dose‐related increases in plasma ACTH levels which were blocked by prior neutralization of endogenous corticotropin‐releasing factor (CRF) but not by vasopressin antibodies. In contrast, the intracerebroventricular (i.c.v.) injection of 50‐µg SIN‐1 released significantly larger amounts of ACTH, a response blunted by either CRF or vasopressin antibodies. While i.c.v. SIN‐1 markedly up‐regulated transcripts of the immediate early gene NGFI‐B in the paraventricular nucleus (PVN) of the hypothalamus, no such response was observed following the i.v. injection of up to 2.0 mg/kg SIN‐1. Finally, we found no evidence that the influence of the peripheral administration of SIN‐1 on ACTH secretion is mediated by altered pituitary responsiveness to CRF or vasopressin. The fact that NO has a profound hypotensive influence in the periphery suggests that it may have released ACTH through this mechanism, although the absence of PVN neuronal response in regions that are activated by decreased blood pressure casts some doubt on this hypothesis. As the systemic injection of arginine derivatives that block NOS activity potently augment the ACTH response to circulating pro‐inflammatory cytokines or vasopressin, the present findings indicate that the mechanisms responsible for this phenomenon are distinct from those responsible for ACTH released by i.v. SIN‐1.
Suppression of Pulsatile Luteinizing Hormone Secretion but Not Luteinizing Hormone Surge in Leptin Resistant Obese Zucker Rats
Authors: Todd B. J. , Ladyman S. R. , Grattan D. R. 
Published: March 2003

AbstractThe adipose tissue‐derived hormone leptin may be a primary mediator linking nutritional status and reproduction. The present study used the leptin‐resistant obese female Zucker rat to investigate whether leptin signalling is required for normal pulsatile luteinizing hormone (LH) secretion and/or generation of the LH surge. For the pulsatile LH secretion study, an indwelling atrial catheter was implanted and a low dose of oestrogen given as a subcutaneous implant to lean and obese ovariectomized (OVX) Zucker rats. One week following OVX, blood samples were collected every 10 min for 3 h during the morning. Plasma LH concentrations were measured by radioimmunoassay. For the LH surge study, lean and obese OVX rats were given a high dose of oestrogen as a subcutaneous implant. Two days later, rats were given progesterone at 09.00 h to induce a proestrus‐like LH surge. Blood samples were collected from an indwelling atrial catheter throughout that and the following day and plasma LH concentrations were measured by radioimmunoassay. LH pulse amplitude and mean LH secretion were profoundly attenuated in obese Zucker rats compared with lean littermates, whereas LH pulse frequency was not significantly different between phenotypes. The opioid receptor antagonist naloxone did not affect the pattern of pulsatile LH secretion in obese rats, suggesting that leptin does not exert its facilitatory effects on LH secretion through an opioidergic pathway. Both lean and obese rats showed characteristic steroid‐induced LH surges. It therefore appears that a leptin signal is required for generation of a normal pattern of pulsatile LH secretion, but is not a necessary component of the steroid‐induced LH surge.
Opioid Receptor Subtypes Involved in the Regulation of Prolactin Secretion During Pregnancy and Lactation
Authors: Andrews Z. B. , Grattan D. R. 
Published: March 2003

AbstractAfferent endogenous opioid neuronal systems facilitate prolactin secretion in a number of physiological conditions including pregnancy and lactation, by decreasing tuberoinfundibular dopamine (TIDA) inhibitory tone. The aim of this study was to investigate the opioid receptor subtypes involved in regulating TIDA neuronal activity and therefore facilitating prolactin secretion during early pregnancy, late pregnancy and lactation in rats. Selective opioid receptor antagonists nor‐binaltorphimine (κ‐receptor antagonist, 15 µg/5 µl), beta funaltrexamine (μ‐receptor antagonist, 5 µg/5 µl) and naltrindole (δ‐receptor antagonist, 5 µg/5 µl) or saline were administered intracerebroventricularly (i.c.v.) on day 8 of pregnancy during a nocturnal prolactin surge, on day 21 of pregnancy during the ante partum prolactin surge or on day 7 of lactation before the onset of a suckling stimulus. Serial blood samples were collected at regular time intervals, via chronic indwelling jugular cannulae, before and after drug administration and plasma prolactin was determined by radioimmunoassay. TIDA neuronal activity was measured using the 3,4‐dihydroxyphenylacetic acid (DOPAC) : dopamine ratio in the median eminence 2 h 30 min after i.c.v. drug injection. In each experimental condition, plasma prolactin was significantly inhibited by both κ‐ and μ‐receptor antagonists, whereas the δ‐receptor antagonist had no effect compared to saline‐injected controls. Similarly, nor‐binaltorphimine and beta funaltrexamine significantly increased the median eminence DOPAC : dopamine ratio during early and late pregnancy, and lactation whereas naltrindole had no effect compared to saline‐injected controls. These data suggest that TIDA neuronal activity, and subsequent prolactin secretion, is regulated by endogenous opioid peptides acting at both κ‐ and μ‐opioid receptors during prolactin surges of early pregnancy, late pregnancy and lactation.
4. Absconding: nurses views and reactions
Authors: Davis Bryn , CLARK N. , KIYIMBA F. , BOWERS L. , JARRETT M. , Mcfarlane L. 
Published: March 2003

Absconding from acute psychiatric wards is common. This paper reports the views of 25 staff nurses working on acute mental health wards in East London about absconding. Interviews explored how staff feel when a patient absconds, the complexities of risk assessment and observation policies, who is blamed when patients abscond and what might reduce absconding.The assessment of the level of risk which a patient posed varied considerably, with some wards using standard risk assessment tools and others talking about their own methods. There was some evidence of conflict with medical staff about what measures should be put in place to manage the risk (observation level, leave). The interviewees were aware of serious consequences of absconding, and this made them worry when patients absconded. Following an abscond most nurses look for an explanation, and this can lead to blame of other members of the team. A sizeable minority spoke of feeling unsupported by their managers, and that their jobs could be at risk following an abscond.The nurses felt that absconding could be reduced through a number of measures, principally raising staffing levels and reducing the reliance on agency nurses.