Principal Transitions Research Articles

Navigating Sudden Transitions in School-Based Leadership

Principal transitions can be disruptive even under the best of conditions, but when a principal is removed, the disruption to the school community can be immense. This case study describes one large, urban elementary school that experienced the forced retirement of a principal after community outrage over discriminatory policies enacted by the principal. This article explores the organizational and interpersonal changes that take place when a principal is removed suddenly. Apiring school and district leaders can engage with this case to simulate managing a crisis caused by a transition in school leadership involving a scandal.

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Acoustic emission and failure characteristics of coal and rock under single-free-face true triaxial loading

The airside roadway is frequently identified as the predominant site for dynamical disasters involving coal and rock. For the assurance of safety in mining zones, it becomes imperative to understand the mechanical response and energy characteristics of the coal and rock system within the airside roadway during mining processes. A triaxial static and dynamic load test system was used to conduct compression experiments on coal and rock samples under single-free-face true triaxial loading at different loading rates. The research findings are summarized as follows: (1) The damage and failure of the samples gradually propagate from the free face to the deeper sections of the samples and evident stage characteristics. Revealed that the damage mechanism was “microfracture localization – localized region development through – overall instability.” (2) A rising loading rate impedes the coal and rock's ability to make adaptive adjustments, thereby amplifying the sample's resistance against crack development, and playing a positive role in stimulating coal and rock failure, and the coal and rock system changed from progressive stable failure to sudden instability failure. The mesoscopic failure pattern gradually evolves into inadequacy and irregularity. (3) Throughout the entire failure episodes of coal and rock samples, the predominant mode of failure is tensile. However, influenced by the loading rate, the principal failure mechanism transitions from tensile to shear during the Ⅳ stage of failure. (4) There is noteworthy congruence between the macrofracture sites and the spatial positioning of high-energy fracture episodes. This furnishing pivotal insights for preempting and control deep impact disasters.

The Impact of Principal Attrition and Replacement on Indicators of School Quality

AbstractTransitions to a new principal are common, especially within urban public schools, and potentially highly disruptive to a school's culture and operations. We use longitudinal data from New York City to investigate if the effect of principal transitions differs by whether the incoming principal was hired externally or promoted from within the school. We take advantage of variation in the timing of principal transitions within an event-study approach to estimate the causal effect of principal changes. Changing principals has an immediate negative effect on student test scores that is sustained over several years regardless of whether hired internally or externally. However, externally hired principals lead to an increase in teacher turnover and a decline in perceptions of the school's learning environment, whereas transitions to an internally promoted principal have no such effects. This pattern of results raises important questions about leadership transitions and the nature of principal effects on school quality.

DEM analysis of passive arching in a shallow trapdoor under eccentric loading

This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models. The numerical models were validated by comparison with laboratory test results. The deformation pattern, soil arching ratio, force chain distribution, and coordination number under various surcharge magnitudes and deviation distances were analyzed. The numerical results showed that the deformation diagram of soil particles can be divided into three zones: principal displacement zone, transition zone, and static zone. With an increase in the surcharge magnitude, the range of the principal displacement zone decreased, but the range of the transition region increased. The curve of the soil arching ratio on the trapdoor can be divided into three phases, which can be well characterized by the tangent modulus. The passive arching effect is degraded by a surcharge. The ultimate soil arching ratio could be approximated as a W-shaped distribution along the +x-direction. With an increase in the trapdoor displacement, the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape. The most powerful force on the trapdoor was mainly distributed on its edge. The average coordination number decreased gradually as the trapdoor moved upward.

Dielectric Properties of Carbon-Like Nanotube Structure: Monte Carlo Study

In this paper, we study the thermal and dielectric properties of a carbon-like nanotube structure. The ferrielectric mixed spin (1,3/2) Blume–Capel Ising model has been investigated, using Monte Carlo simulations under the Metropolis algorithm. We illustrate the thermal and dielectric properties of different physical parameters. Besides, we examine the effects of the exchange coupling interactions, the external longitudinal electric and the crystal fields on the transition temperature. It is found that the polarization decreases toward a transition temperature and undergoing the paraelectric phase, faster for low values of the external longitudinal electric field and the exchange coupling interactions. Besides, the total polarization versus the crystal field undergoes two principal transitions and exhibits a first-order and a second-order transitions.

Assistant Principal Mobility and Its Relationship With Principal Turnover

Assistant principals (APs) are important education personnel, but empirical evidence about their career outcomes remains scarce. Using administrative data from Tennessee and Missouri, we provide the first comprehensive analysis of AP mobility. While prior work focuses on promotions into principal positions, we also examine APs exiting school leadership and transferring across schools. We find yearly mobility rates of 25% to 28%, with 10% of APs leaving school leadership, 7.5% changing schools, and 7.5% to 10% becoming principals. We also document a strong relationship between AP mobility and principal turnover, where higher-performing APs are substantially more likely to replace their departing principal. Finally, principal transitions appear to increase the likelihood that APs exit school leadership and change schools.

Atomic Clocks in Space: A Search for Rubidium and Cesium Masers in M- and L-dwarfs

Abstract I searched for the ground state 6.8 and 9.2 GHz hyperfine transitions of rubidium and cesium toward M- and L-dwarfs that show Rb and Cs optical resonance lines. The optical lines can pump the hyperfine transitions, potentially forming masers. These spin-flip transitions of Rb and Cs are the principal transitions used in atomic clocks (the 133Cs hyperfine transition defines the second). If they are detected in stellar atmospheres, these transitions would provide exceptionally precise clocks that can be used as accelerometers, as exoplanet detectors, as probes of the predictions of general relativity, as probes of light propagation effects, and as a means to do fundamental physics with telescopes. Observations of 21 M- and L-dwarfs, however, show no evidence for Rb or Cs maser action, and a previous survey of giant stars made no Rb maser detections.

Assessment of the impact of land-cover change on water quality: case study of the Chiba watershed, Nabeul, Tunisia

Water scarcity and water quality degradation are important problems that can affect human well-being. Population growth, unplanned urbanization, land-cover change, and the intensification of agricultural and industrial activities are the main reasons for water resource issues. The main aim of this work was to evaluate the effect of land-cover change on groundwater quality in the Chiba watershed, Nabeul, Tunisia. A remote-sensing technique was used to identify the principal transitions in land cover between 1998 and 2018. Additionally, four water quality indicators (electrical conductivity, chloride concentration, nitrate concentration, and sodium absorption ratio) were utilized to investigate variations in water quality in the study area. It was found that most of the watershed was covered with agricultural land in 1998 (87.5%) and 2018 (88.6%). Based on a comparison of these two periods, various types of land-cover transitions were observed. Moreover, the water quality indicators revealed that the salinity hazard and nitrate contamination in the watershed were high. The spatial relationship between water contamination level and land-cover transition category indicated that barren land to built-up land transitions had the strongest negative effect on water quality among all of the main land-cover transitions. Demonstrating the impact of land-cover change on water quality should encourage local decision makers and water managers to implement strategies for sustainable urban planning and periurban agriculture.

Semi-empirical model potential study of Rydberg transitions in gold one-electron spectrum

Semi-empirical model potential calculations of oscillator strengths for Rydberg transitions in principal, sharp and diffuse series of gold one-electron spectrum are presented. Relativistic effects are fully included through solving Dirac equations and core–valence electron correlation is represented in core polarization picture by appropriate part in model potential. The dipole-moment operator of transition is modified in accordance. Systematic trends are investigated in oscillator strengths along the spectral series showing hydrogen-like behavior for large n∗ effective quantum number of upper states of transitions. The so-called Cooper minimum in oscillator strengths is observed for principal series transitions. The influence of core–valence correlation (core polarization) on oscillator strengths along the spectral series is studied in detail​ demonstrating its importance even for transitions to rather highly excited Rydberg states with n≈18. In addition, excitation energies for some levels which positions in the neutral gold spectrum is unknown so far, are also predicted.

Probing diffusive phase transition in Ba(Ti0.80 Zr0.20)O3-0.5(Ba0.70 Ca0.30)TiO3 nanofibers by temperature-dependent piezoelectric force microscopy

Ba(Ti0.80 Zr0.20)O3-0.5(Ba0.70 Ca0.30)TiO3 (BTZ-0.5BCT) nanofibers (NFs) demonstrated diffusive phase transition, resulting in an enhanced Curie temperature TC. As a result, it is scientific significant to probe the variation of ferro/piezoelectricity during such diffusive phase transition region. In this letter, the ferro/piezoelectricity of BTZ-0.5BCT NF was probed by piezoelectric force microscopy (PFM) under a series of temperatures revealing the piezoresponse of BTZ-0.5BCT NF increased with temperatures as the temperature is less than 180°C. The result shows that the first harmonic piezoresponse initially increased with temperatures, yet two singularities appeared at 120 and 180°C, and subsequently rapidly decreased to less than room temperature, demonstrating the corresponding ferroelectric transition process was a diffusive phase transition. Such a diffusive phase transition is caused by the discontinuous internal nanostructure of the NF and the size effect of ferro/piezoelectricity originated from the nano-ceramics. More importantly, the principal ferroelectric phase transition of nano-ceramics during such diffusive phase transition region was further quantified by principal component analysis (PCA) study. This indicates that the principal TC of BTZ-0.5BCT nano-ceramics is around 180°C, representing the TC of the whole BTZ-0.5BCT NF. Such a vivid description of the variated ferro/piezoelectricity with temperatures allows to provide a scientific method to quantify diffusive phase transition by PCA study.

Health needs and access to health care: the case of Syrian refugees in Turkey

ObjectivesTurkey is a principal destination and transit country for refugees from diverse countries. Turkey currently hosts Syrian refugees and provides free access to shelter, education and health care. The aim of this study is to determine the health needs and document the healthcare services available to Syrian refugees in Turkey. Study designLiterature review. MethodsAn examination of the scientific literature, reports and government policies about refugees in Turkey was performed. In addition, literature focussing on the understanding and development of the healthcare needs and systems in crisis situations in Turkey was analysed. ResultsThe Turkish government has made several regulations for Syrian refugees, which allow them to benefit from emergency care units and primary, secondary and tertiary healthcare centres in Turkey's 81 provinces free of charge; the financial costs of these benefits are covered by the Disaster and Emergency Management Authority. Effectiveness of healthcare services for refugees is limited by language barriers, mobility of the refugees and some legal restrictions. Mental health and rehabilitation services are relatively weak because of the inadequate number of qualified practitioners. ConclusionsThe current migration rules in Turkey do not enable refugees to access all human rights. Because the number of refugees has increased, there has been a subsequent increase in the financial and human resources needed for healthcare services. Multidynamic refugee-friendly systems, the provision of preventive health care (including primary and secondary prevention opportunities) and increasing the number of national and international organisations may help improve the health of refugees.

Intrinsic blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dots

Fluorescence blinking of single colloidal semiconductor quantum dots (QDs) has been extensively studied, and several sophisticated models have been proposed. In this work, we derive Heisenberg equations of motion to carefully study principal transition processes, i.e., photoexcitation, energy relaxation, impact ionization and Auger recombination, radiative and nonradiative recombinations, and tunneling between core states and surface states, of the electron-hole pair in single CdSe-CdS/ZnS core-multishell QDs and show that the on-state probability density distribution of the QD fluorescence obeys the random telegraph signal theory because of the random radiative recombination of the photoexcited electron-hole pair in the QD core, while the off-state probability density distribution obeys the inverse power law distribution due to the series of random walks of the photoexcited electron in the two-dimensional surface-state network after the electron tunnels from the QD core to the QD surface. These two different blinking characteristics of the single QD are resolved experimentally by properly adjusting the optical excitation power and the bin time.

Luminescence characteristics of Er3+ ions in ZnO-Ta2O5/Nb2O5/ZrO2-B2O3 glass system- A case study of energy transfer from ZnO to Er3+ ions

Zinc borate glasses doped with 2.0 mol% of Er2O3 and mixed with thermally resistant transition metal oxides viz., Ta2O5, Nb2O5 and ZrO2 were synthesized. Optical absorption and photoluminescence spectra and decay profiles of these glasses were recorded at ambient temperature. The spectra were characterized using Judd–Ofelt theory and various radiative parameters viz., transition probability, A, branching ratio, β, and the radiative lifetime, τ, of principal emission transitions of Er3+ ions in these glasses were evaluated. The results indicated a significant enhancement in the intensity of green emission (related to 4S3/2 → 4I15/2 transition) of Er3+ ions due to co-doping of the glass system with Ta2O5, Nb2O5 and ZrO2. Quantitative analysis of the results pointed out that ZrO2 is the most favorable oxide among the three co-dopants for achieving the highest quantum efficiency of green emission. Results were further analyzed based on the structural modifications taking place in the vicinity of Er3+ ions due to co-doping with Ta2O5, Nb2O5 and ZrO2 and the reasons for such improvement were identified by means of IR and Raman spectroscopy studies. Additionally, the 4S3/2 energy level of Er3+ ions (from which the green emission is originated) seemed to be additionally populated by the energy transfer from the excited state of ZnO and contributed to the amplification of green emission.

Valence band inversion and spin-orbit effects in the electronic structure of monolayer GaSe

Two-dimensional monochalcogenides (MX) have been identified as a unique and promising class of layered materials in recent years. The valence band of single-layer MX, as predicted by theory, is inverted into a bow-shaped (often referred to as an inverted sombrero) and relatively flat dispersion, which is expected to give rise to strongly correlated effects. The inversion leads to an indirect band gap, which is consistent with photoluminescence (PL) experiments, but PL provides no direct evidence of the band inversion in the valence band. Here we demonstrate for a hexagonal MX crystal, gallium selenide (GaSe), using a combination of angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), that the valence band of monolayer (ML) GaSe exhibits a robust inversion of the valence dispersion at the \ensuremath{\Gamma} point forming a bow-shaped dispersion with a depth of 120 \ifmmode\pm\else\textpm\fi{} 10 meV between the double valence band maximum along the \ensuremath{\Gamma}$K$ direction. We also demonstrate that the deeper-lying bands detected in the ARPES spectrum are consistent with DFT calculations only if spin-orbit coupling is considered. The presented ARPES evidence that spin-orbit coupling leads to the splitting of two fourfold-degenerate states into four Kramers doublets is of significance for PL measurements, as the change in energy of the second highest valence state at the \ensuremath{\Gamma} point has a measurable effect on the PL energies in high-energy luminescence. We predict the optical absorption coefficients for the principal transitions in ML GaSe using a four-band $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model parametrized from first-principles theory with spin-orbit effects considered.

Laboratory Rotational Spectra of Silyl Isocyanide

Abstract The rotational spectrum of silyl isocyanide (SiH3NC), an isomer of the well-studied silyl cyanide (SiH3CN), has been detected in the laboratory in a supersonic molecular beam, and the identification was confirmed by observations of the corresponding rotational transitions in the rare isotopic species and SiH3N13C. Spectroscopic constants derived from 19 transitions between 11 and 35 GHz in the three lowest harmonically related rotational transitions in the K = 0 and 1 ladders of the normal isotopic species including the nitrogen nuclear quadrupole hyperfine constant allow the principal astronomical transitions of SiH3NC to be calculated to an uncertainty of about 4 km s−1 in equivalent radial velocity, or within the FWHM of narrow spectral features in the inner region of IRC+10216 near 200 GHz. The concentration of SiH3NC in our molecular beam is three times less than SiH3CN, or about the same as the corresponding ratio of the isomeric pair SiNC and SiCN produced under similar conditions. Silyl isocyanide is an excellent candidate for astronomical detection, because the spectroscopic and chemical properties are very similar to SiH3CN, which was recently identified in the circumstellar envelope of IRC+10216 by Cernicharo et al. and of SiNC and SiCN in the same source.

Influence of modifier oxide on emission features of Sm3+ ion in lithium antimonate glasses

Lithium antimonate glasses doped with 1 mol% of Sm2O3 and mixed with free alkaline earth modifier oxides viz., MgO, CaO and SrO have been synthesized. Optical absorption and luminescence spectra of the prepared glasses were recorded at ambient temperature. The spectra were characterized using Judd–Ofelt theory and the J-O parameters Ω2, Ω4 and Ω6 have been evaluated. The emission spectra (λexc= 401 nm) exhibited four principal emission bands in the visible region corresponding to 4G5/2→6H5/2, 6H7/2, 6H9/2 and 6H11/2 transitions of sm3+ ions. Various radiative parameters viz., transition probability A, branching ratioβ and the radiative lifetime τof principal emission transitions of these glasses have been evaluated. The results indicated a significant enhancement in the intensity of green and orange emissions of Sm3+ ions when the modifier oxide MgO is successively replaced by SrO and CaO. The quantitative analysis of the results has pointed out that CaO mixed glasses is the most favourable oxide among the three modifier oxides for getting the highest luminescence efficiency.

Spectroscopy of Na I and K I atoms embedded in weakly coupled plasma environment

The effect of the plasma environment on the structure and properties of Na I and K I atoms is studied using the Fock-space multireference coupled-cluster theory in the relativistic framework. The Debye-Hückle model is used to account the effect of the plasma environment on the atoms. A significant change in the ionization energies, transition energies, transition probabilities, and oscillator strengths of Na I and K I atoms is seen when they are immersed in plasma. The number of bound states and the binding energies of plasma embedded Na I and K I reduce notably in comparison to the isolated plasma free atoms, and these changes tend the system towards gradual instability. The transition spectra of Na I and K I show red shifts in the presence of plasma screening, whereas the oscillator strengths show the red and blue shifts for the same and different principal quantum number transitions, respectively. Furthermore, the presence of plasma screening causes the suppression of spontaneous transition probabilities of plasma embedded Na I and K I atoms. These results are useful to interpret the spectral lines of astrophysical plasma and to get insights into the physical processes that are operative in the celestial objects.

Diffuse X-ray sky in the Galactic center

Abstract The Galactic diffuse X-ray emission (GDXE) in the Milky Way Galaxy is spatially and spectrally decomposed into the Galactic center X-ray emission (GCXE), the Galactic ridge X-ray emission (GRXE), and the Galactic bulge X-ray emission (GBXE). The X-ray spectra of the GDXE are characterized by the strong K-shell lines of the highly ionized atoms, and the brightest lines are the K-shell transition (principal quantum number transition of n = 2 → 1) of neutral iron (Fe i-Kα), He-like iron (Fe xxv-Heα), and He-like sulfur (S xv-Heα). Accordingly, the GDXE is composed of a high-temperature plasma of ∼7 keV (HTP) and a low-temperature plasma of ∼1 keV, which emit the Fe xxv-Heα and S xv-Heα lines, respectively. The Fe i-Kα line is emitted from nearly neutral irons, and hence the third component of the GDXE is a cool gas (CG). The Fe i-Kα distribution in the GCXE region is clumpy (Fe i-Kα clump), associated with giant molecular cloud (MC) complexes (Sagittarius A, B, C, D, and E) in the central molecular zone. The origin of the Fe i-Kα clumps is the fluorescence and Thomson scattering from the MCs irradiated by past big flares of the supermassive black hole Sagittarius A*. The scale heights and equivalent widths of the Fe i-Kα, Fe xxv-Heα, and Fe xxvi-Lyα (n = 2 → 1 transition of H-like iron) lines are different among the GCXE, GBXE, and GRXE. Therefore, their structures and origins are separately examined. This paper gives an overview of the research history and the present understandings of the GDXE, while in particular focusing on the origin of the HTP and CG in the GCXE.

Influence of Y2O3, Sc2O3 and HfO2 dopants on green emission of Er3+ ions in PbO–Sb2O3 glasses

Lead antimonate glasses doped with 1.0mol% of Er2O3 and co-doped with Y2O3, Sc2O3 and HfO2 were synthesized. Optical absorption and luminescence spectra of the prepared glasses were recorded at ambient temperature. The spectra were characterized using Judd–Ofelt theory and various radiative parameters viz., transition probability A, branching ratio β and the radiative lifetime τ of principal emission transitions of these glasses have been evaluated. The results indicated a significant enhancement in the intensity of green and orange emissions of Er3+ ions due to co-doping of the glass system with Y2O3, Sc2O3 and HfO2. The quantitative analysis of the results pointed out that hafnia is the most favorable oxide among the three co-dopants for getting the highest quantum efficiency of green and orange emissions. The results were further analyzed based on the structural modifications taking place in the vicinity of Er3+ ions due to co-doping with Y2O3, Sc2O3 and HfO2 and the reasons for such improvement have been identified and discussed.