Improved approach to Fowler-Nordheim plot analysis

This article introduces an improved approach to Fowler-Nordheim (FN) plot analysis, based on a new type of intercept correction factor. This factor is more cleanly defined than the factor previously used. General enabling theory is given that applies to any type of FN plot of data that can be fitted using a FN-type equation. Practical use is limited to emission situations where slope correction factors can be reliably predicted. By making a series of well-defined assumptions and approximations, it is shown how the general formulas reduce to provide an improved theory of orthodox FN-plot data analysis. This applies to situations where the circuit current is fully controlled by the emitter characteristics, and tunneling can be treated as taking place through a Schottky-Nordheim (SN) barrier. For orthodox emission, good working formulas make numerical evaluation of the slope correction factor and the new intercept correction factor quick and straightforward. A numerical illustration, using simulated emission data, shows how to use this improved approach to derive values for parameters in the full FN-type equation for the SN barrier. Good self-consistency is demonstrated. The general enabling formulas also pave the way for research aimed at developing analogous data-analysis procedures for non-orthodox emission situations.Comment: Paper is extended version of poster presented at the 25th International Vacuum Nanoelectronics Conference, Jeju island, South Korea, July 2012. Third version includes small changes made at proof correction stag

Illustrating field emission theory by using Lauritsen plots of transmission probability and barrier strength

This technical note relates to the theory of cold field electron emission (CFE). It starts by suggesting that, to emphasize common properties in relation to CFE theory, the term 'Lauritsen plot' could be used to describe all graphical plots made with the reciprocal of barrier field (or the reciprocal of a quantity proportional to barrier field) on the horizontal axis. It then argues that Lauritsen plots related to barrier strength (G) and transmission probability (D) could play a useful role in discussion of CFE theory. Such plots would supplement conventional Fowler-Nordheim (FN) plots. All these plots would be regarded as particular types of Lauritsen plot. The Lauritsen plots of -G and lnD can be used to illustrate how basic aspects of FN tunnelling theory are influenced by the mathematical form of the tunnelling barrier. These, in turn, influence local emission current density and emission current. Illustrative applications used in this note relate to the well-known exact triangular and Schottky-Nordheim barriers, and to the Coulomb barrier (i.e., the electrostatic component of the electron potential energy barrier outside a model spherical emitter). For the Coulomb barrier, a good analytical series approximation has been found for the barrier-form correction factor; this can be used to predict the existence (and to some extent the properties) of related curvature in FN plots.Comment: Based on a poster presented at the 25th International Vacuum Nanoelectronics Conference, Jeju, S. Korea, July 2012. Version 3 incorporates small changes made at proof stag

MAXIMUM POWER TRACKING OF A GRID-CONNECTED WIND-DRIVEN BRUSHLESS DOUBLY-FED RELUCTANCE GENERATOR USING SCALAR CONTROL

This paper presents a scalar volt per hertz (v/f) control technique for maximum power tracking of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG). The proposed generator has two stator windings namely; power winding, directly connected to the grid, and control winding, connected to the grid through a bi-directional converter. The presented control technique is based on the abc-axis and dq-axis dynamic model of BDFRG. A detailed abc-axis and dq-axis dynamic model, by which the dynamic behaviour of the BDFRG can be successfully predicted under different operating conditions, is presented. In addition, a soft starting method is suggested to avoid the over-current of the bi-directional converter. The presented simulation results ensure the effectiveness of the proposed control strategy for maximum wind-power extraction under wind-speed variations

Saudi service users' perceptions and experiences of the quality of their mental health care provision in the Kingdom of Saudi Arabia (KSA): A qualitative inquiry.

This paper presents, as part of a larger mixed-methods design, a study generating a theoretical understanding of issues pertinent to the quality of mental health care in the KSA from the perspective of those using services. Semi-structured interviews were undertaken with thirty service users admitted to inpatient psychiatric wards, using an interview guide developed by the researchers, based on relevant literature. Findings from the thematic analysis showed five themes: (1) The hospital as a prison: a custody versus care dilemma, (2) quality of interactions between staff and service users, (3) quality of services, (4) staff qualities and (5) suggestions for achieving quality of care. A theoretical model drawing upon Donabedian Health Care Model for Evaluating quality of care and the Andersen Behavioural Model of Health Service Use is evident from the data. Structural aspects of care include staff experience and qualifications and key enablers around social and financial support, service users' health needs and status and the physical infrastructure and ward rules. These drive processes of care based upon robust rates of interaction between staff and service users and appear central to quality of mental health care in KSA. Quality of mental health care in KSA is manifested by a therapeutic ethos with a high degree of interaction between professional carers and service users, with the former being highly educated, competent, compassionate, with a high degree of self-awareness, and specialized in mental health. We have uncovered elements of Fanon and Azoulay's 'Cultural Originality' as well as contemporary examples of Goffman's mortification of the self. [Abstract copyright: © 2020 The Authors. International Journal of Mental Health Nursing published by John Wiley & Sons Australia, Ltd on behalf of Australian College of Mental Health Nurses Inc.

Theoretical study of thermoelectric cooling system performance

This work provides a theoretical investigation to study the effect of different operational parameters on theperformance of TE cooling system including the system COP and the rate of heat transfer. The parametersinvestigated are, the applied input power, inlet working fluid velocity, the arrangement of utilized TECs modules andfluid type. The geometry is created with ANSYS multi-physics software as a two-dimensional base case, it isconsisted from two attached horizontal ducts of length (520 mm) and (560 mm), the interface surface between the twoducts contains three thermoelectric modules (4 mm height by 40 mm wide and 40 mm length). The distance betweentwo consecutive thermoelectric modules (150 mm), the inlet and outlet duct diameter (15 mm) and the height of eachduct (10 cm), the inlet voltage to thermoelectric modules ranges from 8.0 V to 12 V and the water inlet velocity to thetwo ducts from 0.001 to 0.01 m/s. Theoretical results showed that the overall COP of TE cooling system is increasedwith the applied input power up to 8.0 W then it decreases with input power up to 18 W after that it takes nearly aconstant value, a noticeable enhancement in the COP is found when the three TECs are in use (Case 10) and the COPof TE cooling system using pure water and nanofluid with 0.05% of nanoparticles as coolants takes the maximumvalue

Long term visual outcomes in laser treated threshold retinopathy of prematurity in Central Saudi Arabia

AbstractPurposeTo assess the long term visual outcomes and refractive status of patients who underwent diode laser for threshold retinopathy of prematurity (ROP) and to investigate the risk factors leading to poor visual outcomes.MethodsFifty-seven patients (114 eyes) with threshold ROP who underwent laser therapy were contacted for reassessment. A chart review was performed for all patients to collect data on visual acuity, retinal status and strabismus. A favorable visual outcome was defined as ⩾20/160 (Snellen acuity) for young adults (cooperative patients), and ⩾CSM for children (uncooperative patients) while unfavorable visual outcome was defined as <20/160 or <CSM. Vision in uncooperative children was graded as central, steady, maintain. Descriptive and inferential analyses were conducted. Chi2 and odds ratios were calculated whenever appropriate. A P value <0.05 was considered as statistically significant.ResultsThe mean age at reassessment was 5.2±2.5years (range, 1–10years) where 36 (63.2%) patients were males and 21 (36.8%) were females. Out Of the 114 laser treated eyes, 73 (64%) were myopic, with mean spherical equivalent (SE) of −6.69 (5.9), range (−0.25 to −21) diaopters, 8 (7%) were emmetrope, while other 33 (29%) were hyperopic with mean SE of +2.43 (3.04), range (+0.25 to +17) diaopters. Strabismus was present in 31 patients (54.4%) of whom 81% (25/31) were esotropic. Retina was found to be normal in 77.1% of the examined eyes, while the remaining eyes had either macular dragging or retinal detachment. Almost 70% of the eyes with a normal retinal examination had favorable visual outcome. Thirteen (11.4%) eyes had zone 1 retinopathy, 83 (72.8%) eyes had zone 2 retinopathy and 2 (1.8%) eyes had zone 3 retinopathy. Vitreous hemorrhage was present in 7 (6.1%) eyes prior to laser treatment. The relationship between final retinal status and visual outcome was statistically significant (P<0.0001). There was no statistically significant correlation between visual outcome and the zone of the retinopathy (P=0.448).ConclusionThe majority of patients who underwent diode laser therapy for threshold ROP had favorable anatomical and visual outcomes. However, high refractive error and strabismus may be clinically the pertinent causes of visual impairment

Shared medical appointments may be effective for improving clinical and behavioral outcomes in type 2 diabetes: A narrative review

Type 2 diabetes mellitus (T2DM) is a complex chronic disease affecting over 400 million people worldwide. Managing T2DM and its associated complications in individual patient consultations poses substantial challenges to physicians due to limited time and resources and lack of access to multidisciplinary teams. Shared medical appointments (SMAs) are consecutive medical consultations provided by a physician in a group setting, where integrated medical care and patient education are delivered in a single session. SMAs allow physicians to deliver the same level of care to multiple patients at the same time, thereby maximizing available resources. However, the effectiveness and practicality of SMAs in the management of T2DM remains unknown. This narrative review summarizes current and emerging evidence regarding the effectiveness of SMAs in improving clinical outcomes in patients with T2DM, as well as whether SMAs are associated with reduced costs and improved diabetes-related behavioral and lifestyle changes. An extensive literature search was conducted on major electronic databases including PubMed and Google Scholar using keywords, including SMAs, group visits, and T2DM to identify all studies of SMAs in patients with T2DM. Studies in type 1 diabetes or mixed or unspecified populations were excluded, as well as studies where SMAs did not involve a physician since these do not meet the classical definition of a SMA. Nineteen studies were identified and are included in this review. Overall, current evidence suggests that SMAs delivered regularly over time may be effective in improving glycemic outcomes, diabetes knowledge, and some diabetes-related behaviors. However, the main limitation of existing studies was the paucity of comparisons with standard care which limits the ability to draw conclusions regarding whether SMAs are superior to standard care in T2DM management. Moreover, the small number of studies and substantial heterogeneity in study designs, populations, and interventions creates difficulties in establishing the practicality and efficiency of SMAs in the clinical care setting. We conclude that there remains a need for larger studies to identify populations who may or may not benefit from the SMA model of care and to clarify the potential benefits and barriers to implementing SMAs into routine diabetes care

Significance of serum levels of angiopoietin-2 and its relationship to Doppler ultrasonographic findings in rheumatoid arthritis patients

AbstractBackgroundAngiopoietin-2 (Ang-2) is connected to angiogenesis in synovial regions, but the significance of its levels in patients with rheumatoid arthritis (RA) is still unclear.Aim of the workTo evaluate the significance of serum levels of Ang-2 in patients with RA. Also, to determine Ang-2 relationship to the findings of joints Doppler ultrasonographic findings.Patients and methodsThis study included 40 patients with RA, and 25 matched healthy controls. All patients were subjected to assessment of pain using visual analogue scale (VAS), assessment of personal activity using the Health Assessment Questionnaire (HAQ) score, and calculation of disease activity score (DAS 28). Laboratory assays of complete blood count (CBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), rheumatoid factor (RF) titre, and measurement of serum levels of Ang-2 by ELISA. Doppler ultrasonography (US) assessment for eight joints, with calculation of synovial thickness and total signal score (TSS), was done.ResultsSerum Ang-2 levels were significantly higher among patients (3191.3±594.9pg/ml) than controls (1771.7±103.1pg/ml) (p<0.001). Serum Ang-2 levels were significantly correlated with ESR, CRP, DAS28, and duration of morning stiffness (p<0.001, p<0.001, p<0.001, and p=0.025, respectively). There was a significant correlation between serum Ang-2 levels and findings of US, regarding joint synovial thickness, and TSS (p<0.001, for both).ConclusionPatients with RA had significantly higher levels of serum Ang-2 versus controls. In those patients, serum Ang-2 levels were significantly correlated with disease activity markers (ESR, CRP), DAS28, and duration of morning stiffness. Moreover, these levels were significantly correlated with synovial thickness, and TSS. The role of Ang-2 in RA pathogenesis might open the door to the development of new therapeutic strategies, particularly which target angiogenesis

Numerical testing by a transfer-matrix technique of Simmons' equation for the local current density in metal-vacuum-metal junctions

We test the consistency with which Simmons' model can predict the local current density obtained for flat metal-vacuum-metal junctions. The image potential energy used in Simmons' original papers had a missing factor of 1/2. Besides this technical issue, Simmons' model relies on a mean-barrier approximation for electron transmission through the potential-energy barrier between the metals. In order to test Simmons' expression for the local current density when the correct image potential energy is included, we compare the results of this expression with those provided by a transfer-matrix technique. This technique is known to provide numerically exact solutions of Schrodinger's equation for this barrier model. We also consider the current densities provided by a numerical integration of the transmission probability obtained with the WKB approximation and Simmons' mean-barrier approximation. The comparison between these different models shows that Simmons' expression for the local current density actually provides results that are in good agreement with those provided by the transfer-matrix technique, for a range of conditions of practical interest. We show that Simmons' model provides good results in the linear and field-emission regimes of current density versus voltage plots. It loses its applicability when the top of the potential-energy barrier drops below the Fermi level of the emitting metal.Comment: Paper accepted for publication in Jordan Journal of Physic

Implementation of the orthodoxy test as a validity check on experimental field emission data

In field electron emission (FE) studies, it is important to check and analyse the quality and validity of experimental current-voltage data, which is usually plotted in one of a small number of standard forms. These include the so-called Fowler-Nordheim (FN), Millikan-Lauritsen (ML) and Murphy-Good (MG) plots. The Field Emission Orthodoxy Test is a simple quantitative test that aims to check for the reasonableness of the values of the parameter "scaled field" that can be extracted from these plots. This is done in order to establish whether characterization parameters extracted from the plot will be reliable or, alternative, likely to be spurious. This paper summarises the theory behind the orthodoxy test, for each of the plot forms, and confirms that it is easy to apply it to the newly developed MG plot. A simple web tool has been developed that extracts scaled-field values from any of these three plot forms, and tests for lack of field emission orthodoxy.Comment: 14 typescript pages, 2 figure