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The COVID-19 pandemic has implications for the postponement of the Simultaneous Pilkades in Indonesia. It's interesting to examine more deeply how the Simultaneous Pilkades policy arrangements during the COVID-19 Pandemic are viewed from the aspect of legal certainty and the legal consequences of postponing the Pilkades during the COVID-19 Pandemic. The research method uses a normative juridical approach with the statute approach and case approach. Legal materials (primary, secondary ,tertiary) were collected through literature study and analyzed in depth using content analysis. Research shows that prior to the pandemic in the laws and regulations the rules regarding the postponement of Simultaneous Pilkades due to force majeure had not been regulated. The authority of the Ministry of Home Affairs to determine the postponement of the Simultaneous Pilkades also has multiple interpretations. The government's policy of issuing the Mendagri Circular is also inaccurate and does not provide legal certainty, the circular is not classified as a statutory regulation. The presence of Permendagri No.72 of 2020 provides legal certainty, the substance clearly regulates the authority of the Regent/Mayor to postpone the Simultaneous Pilkades. The legal consequence of postponing the Pilkades during the Pandemic Period is that many villages will be led by an Acting Village Head. In the future, the provisions regarding the postponement of Simultaneous Village Head Elections due to force majeure are clearly regulated in the legislation and in carrying out tasks by the Acting Village Head must be carried out with full responsibility, because the Acting has the same duties, authorities, obligations and rights as the definitive Village Head. Abstrak Pandemi COVID-19 berimplikasi pada penundaan Pilkades Serentak di Indonesia. Namun pengaturan ihwal penundaan Pilkades Serentak dalam peraturan perundang-undangan ternyata kurang jelas. Menarik untuk mengkaji lebih dalam bagaimana pengaturan kebijakan Pilkades Serentak di masa Pandemi COVID-19 ditinjau dari aspek kepastian hukum dan akibat hukum dari adanya penundaan Pilkades di masa Pandemi COVID-19. Metode penelitian menggunakan yuridis normatif dengan pendekatan perundang-undangan dan pendekatan kasus. Bahan-bahan hukum (primer, sekunder, tersier) dikumpulkan melalui studi kepustakaan dan dianalisa secara mendalam menggunakan metode analisis konten. Penelitian menunjukan bahwa sebelum pandemi dalam peraturan perundang-undangan (UU, PP, Permendagri) aturan mengenai penundaan Pilkades Serentak karena force majeur (bencana non alam) belum diatur. Kewenangan Kemendagri menetapkan penundaan Pilkades Serentak juga multitafsir. Kebijakan pemerintah mengeluarkan Surat Edaran Menteri Dalam Negeri juga kurang tepat dan tidak memberikan kepastian hukum, surat edaran bukan dikelompokkan sebagai sebuah peraturan perundang-undangan. Akhirnya kehadiran Permendagri No. 72 Tahun 2020 memberikan kepastian hukum, subtansinya mengatur secara jelas kewenangan Bupati/Walikota menunda Pilkades Serentak karena situasi darurat COVID-19 serta mekanisme dan teknis pelaksanaan Pilkades Serentak dalam situasi darurat COVID-19. Akibat hukum dari penundaan Pilkades di Masa Pandemi adalah banyak desa yang akan dipimpin oleh seorang Penjabat Kepala Desa. Kedepan ketentuan mengenai penundaan Pilkades Serentak karena force majeur diatur secara jelas dalam peraturan perundangan-undangan dan dalam pelaksanaan tugas oleh Penjabat Kepala Desa harus dilakukan dengan penuh tanggung jawab, karena Penjabat memiliki tugas, wewenang, kewajiban dan hak yang sama seperti Kepala Desa definitif.

We present the case of an 82-year-old woman admitted to a regional emergency general surgery centre with severe left upper quadrant abdominal pain and tenderness within 21 days of receiving the first dose of the ChAdOx1 nCov-19 vaccine (Vaxzevria, AstraZeneca). Following further investigation through CT imaging, a thrombus was discovered in the patient’s splenic artery resulting in a large splenic infarct. Splenic infarcts are rare and it is important to note the association between time of administration of the first dose of vaccine and the occurrence of thromboembolic complications in the noted absence of other risk factors for this condition. We hypothesise a link between Vaxzevria vaccine injection and a rare form of thromboembolic complication: thrombosis of the splenic artery.

Objective: The aim of this study is to compare the unlocked and locked closure of uterine methods regarding control of bleeding and incision healing of uterine. Methodology: This study was conducted in children hospital Faisalabad, and the duration of this study was from April 2019 to December 2019 were recruited for this research work. We measured the count of hemoglobin and levels of serum creatinine of patients in both unlocked (35) and unlocked (47) just before and after 24 hours of surgical intervention. We compared deficit of hemoglobin, enhancement in Creatine Kinase and hemostatic sutures. We also assessed the scar healing of uterine after complete three months. We also compared and calculated the thickness of scar, percentage of scar thinning and niche of both locked (27) and unlocked (32) techniques. Results: There was deficit of hemoglobin in patients of both groups. There was less Creatine Kinase rise in the patients of UG (Unlocked group) but it was not much significant (P value = 0.082). There was need of additional sutures in Unlocked group (P value = 0.016). Niche thickness and percentage of scar thinning site was much low in the patients of Unlocked group (P value = 0.002, P value = 0.000). Conclusions: The unlocked method of uterine closure is very secure and it has very less impairment to myometrium. KEY WORDS: Locked, Unlocked, Thickness, Niche, Incision, Surgical Intervention, Scar, Bleeding, Uterine, Hemoglobin.

Desired Purposes: Purpose of this study is to make the collection of clinical data, clinical presentation and results of the surgical management for the retroperitoneal tumors variably of different types in the children. Design of Study: This study was conducted as prospective study. Venue and Time Frame: We performed our study in Department of Pediatric Surgery, Services Hospital, Lahore having a time frame of almost two and half years starting from Jun, 2016 and finalized in October, 2018. Materials and Methods: This study was accomplished for studying the cases retroperitoneal tumor having the 60 patients for the duration of about 2.5 years. The retroperitoneal tumors that was become the part of our study was of 5 types and comprising on Neuroblastoma (NB), Wilms’ tumors, Rhabdomyosarcoma, On-Hodgkin's Lymphoma (NHL) and Teratoma tumor. Results: Maximum child patients of retroperitoneal tumors were the age of below the five year and typically they were of age in 1st year. Male child patients were in majority than female children. Most commonly, the patients presented with loss of appetite, abdomen anorexia and loss of weight. Wilms’ tumor was found more commonly than other four. Conclusion: Outcomes of our study reflects that prevalence of retroperitoneal tumors was found mostly in the age of five years. Prognostication of retroperitoneal tumors can be improved by initial diagnostics and multimodality management.

Emergency department thoracotomy (EDT) is a potentially life-saving procedure, performed on patients suffering traumatic cardiac arrest. Multiple indications have been reported, but overall survival remains unclear for each indication. The objective of this systematic review is to determine overall survival, survival stratified by indication, and survival stratified by geographical location for patients undergoing EDT across the world. Articles published between 2000 and 2016 were identified which detailed outcomes from EDT. All articles referring to pre-hospital, delayed, or operating room thoracotomy were excluded. Pooled odds ratios (OR) were calculated comparing differing indications. Thirty-seven articles, containing 3251 patients who underwent EDT, were identified. There were 277 (8.5%) survivors. OR demonstrate improved survival for; penetrating vs blunt trauma (OR 2.10; p 0.0028); stab vs gun-shot (OR 5.45; p

Background The prompt recognition of complications is essential in reducing morbidity following anti-reflux surgery. Consequently, many centres employ a policy of routine post-operative contrast studies. The study aimed to examine whether routine contrast studies more effectively recognised early post-operative complications following anti-reflux surgery compared with selective use. Methods This was a retrospective analysis of 240 adults who had undergone primary anti-reflux surgery. Selective use of water-soluble contrast swallows was employed for 115 patients (Group 1) while 125 patients (Group 2) had routine studies. Results 10 (0.9%) patients from Group 1 underwent contrast studies, four (40%) of which were abnormal. Routine studies in Group 2 identified thirty-two abnormalities (27%) however the inter-group difference was not significant (p = 0.32). Only one case from group 2 required immediate re-intervention. This was not statistically significant (p = 0.78). Multivariate analysis found no significant association between selective or routine imaging and re-intervention rates. One patient from group 2 presented three days following discharge with wrap migration requiring reoperation despite a normal post-operative study. Conclusion Routine use of contrast imaging following anti-reflux and hiatus hernia surgery is not necessary. It does not identify a significantly greater number of post-operative complications in comparison to selective use. Additionally, routine use of contrast studies does not ensure the diagnosis of all complications in the post-operative period.

The surface photovoltage spectra (SPS) of a series of ZnSeZnMgSSe multiple quantum wells of different well thickness (15–120 A) have been obtained as a function of temperature (48K < T < 300 K) using a contactless Kelvin probe. In contrast to previous SPS measurements our data were taken using normalized incident light intensity. This normalization procedure has made it possible to fit the numerical derivative of the spectra (with respect to photon energy) to an appropriate lineshape factor to accurately determine the energies of the excitonic transitions. From the splitting between the fundamental conduction to heavy (11H)- and light (11L)-hole transitions as a function of well width we have confirmed the conduction band offset deduced by K. Shahzad et al. [Appl. Phys. Lett., 67, 659 (1995)]. We also have observed an interesting temperature dependence of the intensities of the 11H and 11L SPS features for different well widths.

In this review article, we present photoluminescence and/or Raman scattering properties of ZnSe epitaxial layers which were doped with either nitrogen, oxygen, indium, or lithium. In particular, we present photoluminescence data due to recombination at discrete donor-acceptor pairs in ZnSe epitaxial layers implanted with nitrogen with a dose of 1013 cm-2. The experimental pair data is explained with the help of a theoretical computation of a type-II spectrum involving In donors substituting for Zn and N acceptors for Se. We also report two-hole transitions involving up to 6S 3 2 states of the nitrogen acceptor. The experimental values of the energy positions of these excited states are in good agreement with those obtained using an effective-mass calculation. A sharp line superimposed on the broad donor-acceptor pair band, whose peak position has a constant separation from the excitation energy, is also observed. This separation is ≈0.9 meV larger than the 1S-2S energy spacing for the nitrogen acceptor. We show that this line could be either due to resonant inelastic scattering of the exciting photons by the acceptor impurities, or due to selective excitation of the discrete donor-acceptor pairs. We also present photoluminescence and excitation data to show that oxygen substituting isoelectronically in ZnSe gives rise to a pair of transitions A+ (2.7895 eV) and B (2.7877 eV) as a result of the exchange interaction between the trapped electron-hole pair. The former is attributed to total angular momentum J= 1, Г 4 representation and is electric-dipole allowed while the latter is assigned to J=2 belonging to Г3+Г5 representation and is electric-dipole forbidden. Based on this model, we explain several experimental observations including varying PL intensity of the B line from sample to sample, relatively rapid disappearance of the B line as function of increasing temperature and strong longitudinal-optical (LO) couplings of A+ and B lines. Raman spectroscopy was used to investigate the coupling mechanisms between LO-phonons and electronic excitations in n-type ZnSe layers. The layers, grown by molecular-beam epitaxy, were intentionally doped below the Mott criterion for the insulator-metal transition. The nature of the electron-phonon interaction is determined by the degree of electron localization, which was effectively changed by temperature and donor concentration. The LO-phonons couple to plasmons when electrons are thermally excited into the conduction band or at donor sites. In both cases, unbound phonons are observed. From the renormalized phonon frequencies at high temperature, values of free electron concentration as a function of temperature were established. They are in excellent agreement with Hall-effect determinations. At low temperatures, the phonon Raman profiles are asymmetric and show Fano-type line shapes. The electronic continuum responsible for the phonon self-energies at low temperatures was identified as Raman scattering by bound electrons. In addition, Raman spectroscopy was used to establish the presence of a free hole gas and its coupling to the longitudinal optical phonons in Li-doped ZnSe epilayers. The phonon spectra shift to higher frequencies and broaden with increasing acceptor concentration and temperature, as was the case for indium-doped layers, in accordance with the expectation for coupled phonon-plasmon modes. Values for the concentration and mobility of the holes were obtained from an analysis of the spectral lineshapes. They agree with those determined by other methods. A linear relationships was found between the spectral broadening and the hole concentration. In addition, electronic Raman scattering (ERS) from holes bound to Li acceptors was also studied in ZnSe epilayers and correlated with the net acceptor concentration determined by capacitance versus voltage measurements. The ERS spectra reveal several transitions between the ground 1s and the excited states of the Li acceptors as well as transitions to a continuum of delocalized valence band states. Values of excitation energies for the bound hydrogenic states and the ionization energy of the acceptors were measured. The strength of the ERS signal normalized to the phonon scattering depends linearly on net acceptor concentration.

In-vivo photoacoustic/ultrasound (PA/US) imaging of nude mice was investigated using a photoacoustic imaging system based on a commercial ultrasound scanner HDI-5000. Raw per-channel data was captured and beamformed to generate each individual photoacoustic image with a single laser shot. An ultra-broadband CL15-7 linear array with a center frequency of 8 MHz, combined with a Schott Glass fiber bundle, was used as a compact high resolution imaging probe, with lateral and axial PA resolutions of about 300µm and 200µm, respectively. The imaging system worked in a dual PA-US mode, with the ultrasound outlining the tissue structure and the photoacoustic image showing the blood vessels. PA signals were generated by exposing mice to ultra-short optical pulses from a Nd:YAG-pumped OPO laser operating in a wavelength range of 700-950nm. The corresponding ultrasound images were generated in the regular B-mode with standard delay-and-sum beamforming algorithm. The system resolution was sufficiently high to identify and clearly distinguish the dorsal artery and the two lateral veins in the mouse tail. Both the saphena artery and the ischiatic vein on the cross-section of the mouse leg were clearly outlined in the PA images and correctly overlaid on the ultrasound image of the tissue structure. Similarly, cross-section PA images of the mouse abdomen revealed mesenteric vasculatures located below the abdominal wall. Finally, a successful PA imaging of the mouse thoracic cavity unveiled the ascending and descending aorta. These initial results demonstrate a great potential for a dual photoacoustic/ultrasound imaging modality implemented on a commercial ultrasound imaging scanner.

Photoacoustic (PA) experiments were performed using a modified commercial ultrasound scanner equipped with an array transducer and a Nd:YAG pumped OPO laser. The contrast agent SIDAG (Bayer Schering Pharma AG, Germany), used to enhance the optical absorption, demonstrated an expected pharmacokinetic behavior of the dye in the tumor and in the bladder of the nude mice. A typical behavior in the tumor consisted of an initial linear increase in PA signal followed by an exponential decay. PA signal approached the pre-injection level after about one hour following the dye injection, which was consistent with the behavior for such contrast agents when used in other imaging modalities, such as fluorescence imaging. The in-vivo spectral PA data from the mouse bladder, conducted 1.5 hours after the dye injection, clearly demonstrated presence of the dye. The multi-spectral PA data was obtained at 760nm, 784nm and 850nm laser excitations. The PA intensities obtained at these three wavelengths accurately matched the dye absorption spectrum. In addition, in the kidney, a clearance organ for this contrast agent, both in-vivo and ex-vivo results demonstrated a significant increase (~ 40%) in the ratio of PA signal at 760nm (the peak of the dye absorption) relative to the signal at 850nm (

We studied the nature of photoacoustic signals that were generated under a variety of conditions from vessel-mimicking polyethylene tubes. The vessels, filled with a range of contrast agents, were buried in tissue-like phantoms that possessed low to high optical absorption and scattering properties. In a photoacoustic image, we observed that either a single spot or two distinct spots could represent a single vessel depending on the strength of the infused contrast agent and on the size of the vessels. We typically found linear increase of the photoacoustic intensity with laser excitation power as well as with absorption coefficient of the contrast agent. However, we found that there is an optimum excitation power for achieving the best photoacoustic signal. If a vessel is buried in a highly absorbing background, increasing the laser power beyond a certain limit reversibly reduces the photoacoustic signal from the vessel, eventually decreasing it to zero. We also studied the blood-to-tissue absorption contrast requirement for observing the photoacoustic signal from a vessel buried in an absorbing and scattering tissue. We find that, in order to distinguish the photoacoustic signal from its background, the absorption coefficient of contrast agent in the vessel must be at least 2.5 times larger than that of the surroundings.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The coupling mechanisms between longitudinal-optical phonons and electronic excitations in n-type ZnSe layers were investigated with Raman spectroscopy in conjunction with transport measurements. The layers were grown by molecular-beam epitaxy and were intentionally doped below the Mott criterion for the insulator-metal transition. The nature of the electron-phonon interaction is determined by the degree of electron localization, which was effectively changed by temperature and donor concentration. The longitudinal-optical phonons couple to plasmons when electrons are thermally excited into the conduction band and to a continuum of electronic excitations when electrons are localized in an impurity band or at donor sites. In both cases unbound phonons are observed. From the renormalized phonon frequencies at high temperature, values of free-electron concentration as a function of temperature were established. They are in excellent agreement with Hall-effect determinations. At low temperatures the phonon Raman profiles are asymmetric and show Fano-type line shapes. The electronic continuum responsible for the phonon self-energies at low temperature was identified as Raman scattering by bound electrons.

We studied, by photoluminescence (PL) and PL excitation spectroscopies, unintentionally doped ZnSe epilayers, grown by molecular beam epitaxy using ultra-high-purity sources of zinc and selenium. We find that the PL from such samples is dominated by free excitonic transitions with weak contributions from transitions due to donor-bound excitons. In particular, we discuss a possible origin of a peak I0v located at 22380 cm-1 (2.7738 eV). Selective PL and PL excitation experiments conclusively show that I0v is due to an independent transition and not related to excitonic processes. We also find that as we increase Zn/Se beam pressure ratio, an increase in the intensity of I0v is observed. In addition, the coupling constant for I0v to LO phonons is found to be ≈0.04 which is very weak considering the fact that its localization energy of ≈29 meV is very large. These observations together with the fact that the full width at half maximum for I0v is ≈2 meV, which is large compared to

In this review article, we describe detailed optical properties of ZnSe-ZnSxSe1-x strained-layer superlattices (SLS) grown on GaAs substrates by molecular beam epitaxy. Photoluminescence and excitation measurements were carried out to study effects of the strain and carrier confinement in this strained layer system. For the case where the total thickness of SLS is very small (∼1000A) compared to its critical thickness, the structure grows pseudomorphic with the ZnSe buffer layer. In this case the ZnSe well layers are not strained and all the blue shift in the optical spectra is attributed to the carrier confinement effects only. At the other extreme, for the case of a SLS with very large total thickness (∼4 μm), we show that it can be treated as free standing with the ZnSe layers under in-plane biaxial compression and the ZnSxSe1-x layers under biaxial tension. In the intermediate cases of total thicknesses, we show that SLSs are not fully relaxed to their equilibrium states by measuring the strains directly in the well layers. We also present photoluminescence data to show that SLSs grown on ZnSe buffer layers can exist in a continuous range from a perfectly coherent state to a totally free standing state as the total thickness of the SLS increases. In addition, we also observe the effect of strain produced by the SLS on the buffer layers. We also discuss in detail the depth dependence of the strains in a given SLS or a heteroepilayer by using Raman scattering measurements performed under laser excitation below and above the band gap. We find that the strain values near the top surface are driven by a stronger relaxation of the in-plane lattice constants towards equilibrium. Empirical values for the band offsets are obtained from the analysis of optical response as a function of the sample parameters. Theoretical calculations of the band offsets, based on the model-solid approach, were also performed and are found to agree with the experimental observations to within 0.05 eV. They indicate that all possible ZnSe-ZnSxSe1-x interfaces will exhibit a very small conduction band offset. We also carried out resonant Raman-scattering experiments at low temperatures to study the optical modes of these SLS systems. The observed Raman modes can be classified into two groups: one corresponds to vibrations with amplitudes localized either in the ZnSe or in the ZnSxSe1-x layers. These are confined modes. In the second group, the phonons with amplitudes in both layers are included, namely, interface vibrations and folded optical modes. The measured dependence of the confined and delocalized phonons on sample parameters (individual layer thicknesses, superlattice period, total superlattice thickness, and interfacial strain) and on resonant excitation is presented and discussed in detail. The trends that were established are compared with the theoretical predictions of lattice dynamic models for multilayer structures. Experimental data on the lattice dynamic properties of ZnSxSe1-x alloys are included for comparison purposes and to distinguish unequivocally superlattice effects. These data were gathered with ternary layers grown and measured under similar conditions as the superlattices. Concomitant with vibrational characteristics, this work has also yielded an insight into other intrinsic properties of SLSs. The interplay between confinement and strain in the renormalization of phonon frequencies was elucidated from an experimental point of view and this information was applied to characterize the nature of superlattice transition from pseudomorphic to free standing.

Protein nanospheres capable of frequency controlled oscillation in response to laser stimulation are presented as contrast agents for photoacoustic imaging. Incident laser energy absorbed by dye-labeled protein nanospheres causes thermoelastically generated sound production. Plotted A-line graphs reveal a distinctive morphology and greater than 2 orders of magnitude increase in signal amplitude subsequent to converting labeled proteins into nanospheres. Evidence of nonlinearity and enhancement of ultrasound backscatter indicate a potential use in contrast-enhanced harmonic imaging. Photoacoustic and ultrasound imaging of protein nanospheres in phantom vessels show enhanced contrast at low concentration and clear delineation of the phantom vessel wall.

We use a theoretical model of semiconductor lasers to calculate threshold current density (Jth), optical gain (g), and spontaneous emission rate (rsp) as a function of the two heterojunction band offsets between Zn1−uCduSe(well)/ZnSzSe1−z(guiding) layers and ZnSzSe1−z (guiding)/ Zn1−xMgxSySe1−y(cladding) layers. We find that for the conduction‐band offset between the well and the guiding layers ranging from ∼0.55ΔEg to ∼0.75ΔEg (ΔEg being the energy band‐gap difference), there is very little change in Jth, g, rsp. Furthermore, these three quantities are very weakly dependent on the conduction‐band offset between the guiding and the cladding layers ranging from 0.2ΔEg to 0.5ΔEg. However, if the offset between the well and the guiding layers is increased from ∼0.75ΔEgto ∼0.8ΔEg, the calculations indicate a sharp drop in Jth, g, and rsp. We explain this behavior as due to the unbinding of the ground‐state light‐hole subband as the valence band offset is reduced.

Carrier confinement in blue‐green II–VI semiconductor lasers was investigated. For devices longer than 300 μm an energy barrier of 260–280 meV was found to confine the electrons, the carrier being mainly responsible for leakage, within the active region. Shorter devices show more leakage due to an increased importance of mirror losses which require higher threshold gain. Due to the low conductivity of the p‐type cladding layer there is a sizable contribution of drift to the total leakage current.

We present an analysis of optical data from ZnSe strained‐layer quantum wells surrounded by Zn1−xMgxSySe1−y barrier layers to extract the band offsets. If we use only the ground state transitions from our experimental data, no unique value of the offset can be obtained: a direct consequence of the fact that there are no uniquely agreed upon values of the effective masses for ZnSe available. However, if we include the excited states, only one out of six considered sets of effective masses gives a reasonable fit to the experimental data, giving the conduction band offset of only 10% of the band gap difference.

We report a novel technique to obtain p‐type ZnSe layers doped with nitrogen. The layers were grown in a low‐pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance‐voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor‐acceptor pair spectra were also observed.

Electronic Raman scattering (ERS) from holes bound to Li acceptors was studied in ZnSe layers and correlated with the net acceptor concentration NA−ND determined by capacitance versus voltage measurements. The layers were grown by molecular beam epitaxy on GaAs substrates and were doped in situ to NA−ND concentrations ranging from high 1015’s to low 1017’s cm−3. The ERS spectra reveal several transitions between the ground 1S and shallower S and P bound states of the Li acceptors as well as transitions to a continuum of delocalized valence‐band states. Values of excitation energies for the bound hydrogenic states and the ionization energy of the acceptors were measured. The strength of the ERS signal normalized to the phonon scattering depends linearly on NA−ND. This relationship can be exploited in contactless characterization of p‐type ZnSe.

We present low‐temperature photoluminescence and transmission electron microscopy data to show that two transitions I0V at ∼2.774 eV and Y0 at ∼2.60 eV, frequently observed in unintentionally doped zinc selenide epitaxial layers, are directly related to structural defects. It is shown that these transitions are strong in those samples which have very low background impurities and high density of structural defects and weak in those cases that have either high background impurities or low density of structural defects.

The growth of zinc selenide by molecular beam epitaxy using a cracked selenium source is studied. It is found that high quality growth can be achieved at substantially lower substrate temperatures than has been possible using uncracked selenium sources. It is determined from reflection high‐energy electron diffraction observations that the use of cracked selenium produces growth dominated by a two‐dimensional mechanism at substrate temperatures as low as 225 °C and that exposure of the GaAs substrate to cracked selenium prior to the initiation of growth has a substantial effect on the GaAs substrate and the early stages of ZnSe growth.

In this letter we investigate the influence of self‐absorption on the excitonic emission spectra of ZnSe epitaxial layers grown by molecular beam epitaxy on GaAs substrates. We observe that, very often, samples grown under identical conditions show a widely ranging ratio of neutral donor‐bound‐exciton to free‐exciton intensities in photoluminescence (PL). We present experimental evidence to show that these differences can arise from the variations in the epilayer thickness and detailed PL experimental conditions and do not necessarily represent the layer‐to‐layer purity fluctuations, as the spectral line shapes may suggest.

An ultrasound imaging technology based on electrowetting has been developed and integrated in a miniaturized ultrasound scanner. The feasibility of scanning the ultrasound beam of a single-piston transducer in a three-dimensional space by using electrowetting is demonstrated. The technology has a high potential to be embedded in devices where size restrictions do not allow the use of traditional ultrasound phased-array transducers.

Dye-labeled protein microspheres, submicron in size and capable of producing thermoelastically generated ultrasound in response to laser stimulation, are presented as contrast agents for photoacoustic imaging. Incident laser energy absorbed by fluorescein isothiocyanate (FITC)-labeled elastin submicrospheres results in thermoelastically generated sound production. Plotted A-line graphs reveal a distinctive morphology and a greater than two orders of magnitude increase in signal amplitude subsequent to converting FITC elastin into submicrospheres (despite a four orders of magnitude decrease in concentration). Evidence of nonlinearity and enhancement of ultrasound backscatter indicate a potential use in contrast-enhanced harmonic imaging. Photoacoustic and ultrasound imaging of FITC-elastin submicrospheres in a water-filled phantom vessel shows enhanced contrast at low concentration and clear delineation of the phantom vessel wall.

We present photoluminescence (PL) and excitation data to show that oxygen substituting isoelectronically in ZnSe gives rise to a pair of transitions ${\mathit{A}}^{+}$(2.7895 eV) and B (2.7877 eV) as a result of the exchange interaction between the trapped electron-hole pair. The former is attributed to total angular momentum J=1, ${\mathrm{\ensuremath{\Gamma}}}_{4}$ representation, and is electric dipole allowed while the latter is assigned to J=2 belonging to the ${\mathrm{\ensuremath{\Gamma}}}_{3}$+${\mathrm{\ensuremath{\Gamma}}}_{5}$ representation and is electric dipole forbidden. Based on this model, we explain several experimental observations including varying PL intensity of the B line from sample to sample, the relatively rapid disappearance of the B line as a function of increasing temperature, and strong LO couplings of the ${\mathit{A}}^{+}$ and B lines.

Visible light emission from porous silicon has recently been demonstrated by several groups. We have found that annealing of porous silicon samples in an inert atmosphere over 250C reduces the emission intensity, almost fully quenching it by 450C. We believe that this is due to the removal of passivating hydrogen, based on measurements of infrared absorption due to Si-H vibrational modes. We have also found that we can partially recover the emission intensity in these annealed porous silicon layers by passivation in a hydrogen plasma. We have therefore demonstrated that hydrogen passivation is necessary for the observation of visible emission from porous silicon. We have also shown that thermal oxidation of porous silicon over 200C reduces the PL emission. We propose that this reduction is also due to the loss of hydrogen passivation during the oxidation.

P-type conduction in bulk ZnSe has been achieved using 1×1016 cm−2 nitrogen (N) ionimplantation followed by a high temperature rapid thermal annealing. Room temperature Hall effect measurements of the sample show that the hole concentration is ∼1×1017 cm−3, and the mobility is ∼30 cm2/V-s. Photoluminescence (PL) measurements were performed to study the optical behavior of the samples, and the results show that the ion implantation damage can be partially repaired by thermal annealing at 900°C or higher. Thermal degradation and recovery of the ion-implantation damage were studied as a function of the annealing temperature.

On presente des donnees de photoluminescence dues a la recombinaison a des paires donneur-accepteurs discretes dans ces couches epitaxiales implantees avec de l'azote a 10 13 cm −2 . Les donnees experimentales sont expliquees a l'aide d'une simulation theorique d'un spectre de type II impliquant des donneurs In se substituant a Zn et les accepteurs N a Se. Observation d'une raie superposee a la bande de paire accepteur-donneur. Cette raie semble due a la diffusion inelastique resonnante des photons excites ou a l'excitation selective des paires accepteur-donneur

Photoluminescence (PL) measurements have been carried out in hydrogenated and as deposited polycrystalline silicon thin films deposited on quartz substrates. Behavior of the PL spectrum as a function of temperature and intensity in the hydrogenated samples is reported. A mechanism that provides a qualitative explanation for the observed PL results is described. In the unhydrogenated sample the signal was much weaker and we were unable to observe any signals over an appreciable range of intensity and temperatures. The cause for much lower signals in the unhydrogenated sample is most likely due to higher surface recombination velocity.

— By using light-guide components, a new scrolling-color engine for single-panel LCoS projection has been developed. Light guides allow for loss-less delivery of light leading to a simpler and more-compact system. Engine design and construction based on a single 0.88-in.-diagonal LCoS panel is described. Separate results with a multilayer optical film Cartesian PBS show that a significant improvement in system efficiency is possible.

— In an LCOS projection system, a wire-grid PBS may be used to improve contrast and a field lens may be employed to simplify the projection lens. However, the combination of the two leads to a reduced contrast, which decreases with increasing field angle in one direction. In a representative arrangement, measured contrast with a mirror varied from over 10,000 in the center to 450 at the left and right edges. Contrast loss can be improved with a weaker field lens. The problem arises due to a phase delay between polarization states introduced by the wire grid. Polarization measurements show a +53-nm phase delay with an axis parallel to the wire-grid surface normal. Various compensation schemes are proposed in order to reduce the aforementioned loss of contrast.

In projection applications, as the liquid crystal device size continues to shrink, more demand is placed on the illumination optics to increase lumens per unit area on the device. One method to achieve this is to use smaller f-numbers (larger cone angles); however, as the f-number of the optical system reduces the contrast invariably suffers. In this paper, we examine a twisted nematic liquid on silicon device (90TN0, LCoS) and explore the trade-off between contrast and system f-number. This mode is nominally self-compensating, however additional compensation of the off-axis birefringence is required to achieve higher contrast, especially at lower f-numbers (