Emergence of liquid following laser melting of gold thin films.

X-ray structural science is undergoing a revolution driven by the emergence of X-ray Free-electron Laser (XFEL) facilities. The structures of crystalline solids can now be studied on the picosecond time scale relevant to phonons, atomic vibrations which travel at acoustic velocities. In the work presented here, X-ray diffuse scattering is employed to characterize the time dependence of the liquid phase emerging from femtosecond laser-induced melting of polycrystalline gold thin films using an XFEL. In a previous analysis of Bragg peak profiles, we showed the supersonic disappearance of the solid phase and presented a model of pumped hot electrons carrying energy from the gold surface to scatter at internal grain boundaries. This generates melt fronts propagating relatively slowly into the crystal grains. By conversion of diffuse scattering to a partial X-ray pair distribution function, we demonstrate that it has the characteristic shape obtained by Fourier transformation of the measured F(Q). The diffuse signal fraction increases with a characteristic rise-time of 13 ps, roughly independent of the incident pump fluence and consequent final liquid fraction. This suggests the role of further melt-front nucleation processes beyond grain boundaries.

The prevalence of dental caries and associated factors among students living with disability in the Amhara region, Ethiopia.

OBJECTIVES: People living with disability are more vulnerable to dental caries and have a high decayed, missed, and filled permanent teeth (DMFT) index and untreated dental disease than nondisabled individuals. In Ethiopia, there is a dearth of information on the oral health status of the disabled population. Hence, this study aimed to determine the prevalence of dental caries and its predictors among special needs school students in the Amhara region, Ethiopia. METHODS: An institution-based cross-sectional study was done on special needs school students in the Amhara region from November 2020 to April 2021. The study participants were recruited using a simple random sampling technique using a computer random generator. Data collection was done using the World Health Organization oral health survey tool. Data entry was done using Epi-data 4.6 and analyzed using SPSS 26. A logistic regression model was used to identify the possible predictors of dental caries. RESULTS: Four hundred and forty-three students with a mean age of 15.8 ± 3.8 were included in the study. The prevalence of dental caries was 41.5% (95% confidence interval [CI]: 36.3, 46.0) in permanent dentition with a mean DMFT score of 1.3 ± 1.6. The prevalence of dental caries in primary dentition was 23.1% (95% CI: 11.9, 32.1) with a mean decayed, missed, and filled primary teeth (dmft) score of 1.9 ± 0.2. Being 7-12 years old (adjusted odds ratios [AOR] = 3.6, 95% CI: 1.6, 8.3), lower grade level (AOR = 2.4, 95% CI:1.3,4.4), poor oral hygiene status (AOR = 2.5, 95% CI: 1.3, 4.8), and lack of parental support during tooth brushing (AOR = 2.2, 95% CI: 1.2, 4.1) were independent predictors of dental caries. CONCLUSIONS: A significant amount of special needs school students in the study area had dental caries. Age, grade level, oral hygiene status, and lack of parent support during tooth brushing were independent predictors of dental caries.

The impact of rainfall distribution methods on streamflow throughout multiple elevations in the Rocky Mountains using the APEX model-Price River watershed, Utah.

The hydrology of mountainous watersheds in the western United States is significantly influenced by snow year-round. It is widely known that topography affects precipitation; however, the knowledge of how watershed rainfall designation methods affect streamflow is not well understood for high-relief areas. The objectives of this study were to assess the predictive capability of the Agricultural Policy/Environmental eXtender (APEX) model to simulate streamflow in a snowmelt-dominated watershed with high spatial rainfall variability through (a) allocating weather stations to sub-basins based on a conventional Thiessen polygon method (CM) or a rainfall-elevation-based input (RE) and using an areal average Parameter-Elevation Regression on Independent Slopes Model (PRISM) rainfall designation and (b) improving the snowmelt processes in the Price River watershed, Utah. The updated APEX model with snowmelt parameters significantly improved spring flood simulation. The RE was the most robust method in snowmelt and seasonal streamflow simulations compared with the CM and PRISM rainfall designations. Adapting the APEX model to simulate snow-dominant complex terrains will provide crucial water quantity and quality predictions for reliable environmental and watershed management assessment.

Laser-induced transient magnons in Sr3Ir2O7 throughout the Brillouin zone.

Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic X-ray scattering we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in gapped antiferromagnets and that they persist for several picoseconds, which is opposite to what is observed in nearly gapless magnets. Our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism.

Site-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy*.

Time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [IrIII (ppy)2 (bpy)]+ photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe3(CO)12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.

Structure of a seeded palladium nanoparticle and its dynamics during the hydride phase transformation.

Palladium absorbs large volumetric quantities of hydrogen at room temperature and ambient pressure, making the palladium hydride system a promising candidate for hydrogen storage. Here, we use Bragg coherent diffraction imaging to map the strain associated with defects in three dimensions before and during the hydride phase transformation of an individual octahedral palladium nanoparticle, synthesized using a seed-mediated approach. The displacement distribution imaging unveils the location of the seed nanoparticle in the final nanocrystal. By comparing our experimental results with a finite-element model, we verify that the seed nanoparticle causes a characteristic displacement distribution of the larger nanocrystal. During the hydrogen exposure, the hydride phase is predominantly formed on one tip of the octahedra, where there is a high number of lower coordinated Pd atoms. Our experimental and theoretical results provide an unambiguous method for future structure optimization of seed-mediated nanoparticle growth and in the design of palladium-based hydrogen storage systems.

Publisher's Note: Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated [Co(terpy)_{2}]

This corrects the article DOI: 10.1103/PhysRevLett.117.013002.

The yield of community-based tuberculosis and HIV among key populations in hotspot settings of Ethiopia: A cross-sectional implementation study.

OBJECTIVE: To determine the yield of tuberculosis (TB) and the prevalence of Human Immuno-deficiency virus (HIV) among key populations in the selected hotspot towns of Ethiopia. METHODS: We undertook a cross-sectional implementation research during August 2017-January 2018. Trained TB focal persons and health extension workers (HEWs) identified female sex workers (FSWs), health care workers (HCWs), prison inmates, homeless, internally displaced people (IDPs), internal migratory workers (IMWs) and residents in missionary charities as key and vulnerable popuaiton. They carried out health education on the importance of TB screening and HIV testing prior to recruitment of the study participants. Symptomatic TB screening and HIV testing was done. The yield of TB was computed per 100,000 background key population. RESULTS: A total of 1878 vulnerable people were screened, out of which 726 (38.7%) presumptive TB cases and 87 (4.6%) TB cases were identified. The yield of TB was 1519 (95% CI: 1218.1-1869.9). The highest proportion (19.5%) and yield of TB case (6,286 (95% CI: 3980.8-9362.3)) was among HCWs. The prevalence of HIV infection was 6%, 67 out of 1,111 tested. IMWs and FSWs represented 49.3% (33) and 28.4% (13) of the HIV infections, respectively. There was a statistically significant association of active TB cases with previous history of TB (Adjusted Odds Ratio (AOR): 11 95% CI, 4.06-29.81), HIV infection (AOR: 7.7 95% CI, 2.24-26.40), and being a HCW (AOR: 2.42 95% CI, 1.09-5.34). CONCLUSIONS: The prevalence of TB in key populations was nine times higher than 164/100,000 national estimated prevalence rate. The prevalence of HIV was five times higher than 1.15% of the national survey. The highest yield of TB was among the HCWs and the high HIV burden was detected among the FSWs and IMWs. These suggest a community and health facility based integrated and enhanced case finding approaches for TB and HIV in hotspot settings.

Ultrafast x-ray diffraction study of melt-front dynamics in polycrystalline thin films.

Melting is a fundamental process of matter that is still not fully understood at the microscopic level. Here, we use time-resolved x-ray diffraction to examine the ultrafast melting of polycrystalline gold thin films using an optical laser pump followed by a delayed hard x-ray probe pulse. We observe the formation of an intermediate new diffraction peak, which we attribute to material trapped between the solid and melted states, that forms 50 ps after laser excitation and persists beyond 500 ps. The peak width grows rapidly for 50 ps and then narrows distinctly at longer time scales. We attribute this to a melting band originating from the grain boundaries and propagating into the grains. Our observation of this intermediate state has implications for the use of ultrafast lasers for ablation during pulsed laser deposition.

Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity.

Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving interest in new means of probing their mechanisms. Using a combination of time-resolved x-ray absorption spectroscopy and hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations and x-ray absorption near-edge spectroscopy calculations, we elucidate the mechanism of photoaquation in the model system iron(ii) hexacyanide, where UV excitation results in the exchange of a CN- ligand with a water molecule from the solvent. We take advantage of the high flux and stability of synchrotron x-rays to capture high precision x-ray absorption spectra that allow us to overcome the usual limitation of the relatively long x-ray pulses and extract the spectrum of the short-lived intermediate pentacoordinated species. Additionally, we determine its lifetime to be 19 (±5) ps. The QM/MM simulations support our experimental findings and explain the ∼20 ps time scale for aquation as involving interconversion between the square pyramidal (SP) and trigonal bipyramidal pentacoordinated geometries, with aquation being only active in the SP configuration.

Using Ultrafast X-ray Spectroscopy To Address Questions in Ligand-Field Theory: The Excited State Spin and Structure of [Fe(dcpp)2]2.

We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)2]2+ (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the 5T2/3T1 crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kß X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the 5T2 state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a 5T2 state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited 5T2 state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin 1A1 ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.

Impacts of social indicators on assessing the recovery potential of impaired watersheds.

An analysis was carried out to understand how watersheds' potential for restoration was impacted by social indicators. This study employed the USEPA Recovery Potential Screening tool, a decision support system, to compare 51 watersheds in the state of Mississippi, USA, using ecological, stressor, and social indices, and the recovery potential integrated (RPI) index. An in-depth analysis was performed on four watersheds in the Delta region of Mississippi (Lake Washington, Harris Bayou, Steele Bayou, and Coldwater River), each impaired by sediments and nutrients. Sixteen social indicators were categorized into three subcategories: Socio-Economic, Organizational, and Informational. Watersheds with lower social indices had lower RPI scores. In the particular watersheds studied, the Socio-Economic subcategory was observed to be the most impactful to the overall recovery potential when compared to the other two social subcategories. As a sensitivity analysis, a "what if" simulation was performed to explore alternatives to upgrade a watershed's social index and, consequently, the relative recovery potential of the watershed to a target level. This analysis is useful for understanding how particular social indicators of a community impact the relative potential for recovering a watershed, beyond just the ecological and stressor conditions. It also sheds light on assessing which social indicators can be improved.

Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy.

We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]2+ in solution to gain deeper insight into the Fe-ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide variety of environments. A picosecond-time-resolved measurement of the complete 1s X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitals directly involved in the light-driven dynamics; a change in the metal-ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations and more subtle features at the highest energies reflect changes in the frontier orbital populations.

A multi-MHz single-shot data acquisition scheme with high dynamic range: pump-probe X-ray experiments at synchrotrons.

The technical implementation of a multi-MHz data acquisition scheme for laser-X-ray pump-probe experiments with pulse limited temporal resolution (100 ps) is presented. Such techniques are very attractive to benefit from the high-repetition rates of X-ray pulses delivered from advanced synchrotron radiation sources. Exploiting a synchronized 3.9 MHz laser excitation source, experiments in 60-bunch mode (7.8 MHz) at beamline P01 of the PETRA III storage ring are performed. Hereby molecular systems in liquid solutions are excited by the pulsed laser source and the total X-ray fluorescence yield (TFY) from the sample is recorded using silicon avalanche photodiode detectors (APDs). The subsequent digitizer card samples the APD signal traces in 0.5 ns steps with 12-bit resolution. These traces are then processed to deliver an integrated value for each recorded single X-ray pulse intensity and sorted into bins according to whether the laser excited the sample or not. For each subgroup the recorded single-shot values are averaged over ∼107 pulses to deliver a mean TFY value with its standard error for each data point, e.g. at a given X-ray probe energy. The sensitivity reaches down to the shot-noise limit, and signal-to-noise ratios approaching 1000 are achievable in only a few seconds collection time per data point. The dynamic range covers 100 photons pulse-1 and is only technically limited by the utilized APD.

Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated [Co(terpy)_{2}]

We study the structural dynamics of photoexcited [Co(terpy)_{2}]^{2+} in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of the high spin state is established on a single-picosecond time scale and that this state has a lifetime of ∼7 ps.

Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species.

X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emission spectroscopy (XES) of the strongest core-to-core emission lines (Kα and Kß) is now being utilized. Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit. In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES for time-resolved experiments. We discuss technical improvements that will make valence-to-core XES a practical pump-probe technique.

Predictors of dental caries among children 7-14 years old in Northwest Ethiopia: a community based cross-sectional study.

BACKGROUND: Dental caries in children remains a significant public health problem. It is a disease with multifactorial causes. The aim of the study was to assess the prevalence and associated factors of dental caries among children between 7 to 14 years old. METHODS: A community based cross-sectional study was conducted in Gondar town from June 2011 to September 2011. A total of 842 children were involved in the study. Multi-stage sampling technique was used to select the children. Pretested and structured questionnaires were used to collect data from mothers. Clinical examination of children was done using dental caries criteria set by world health organization. Data were entered, cleaned and edited using EPI Info version 3.5.1 and exported to SPSS version 16.0 for analysis. Binary multiple logistic regression analyses was applied to test the association. RESULTS: Four hundred sixty three (55%) children were females. The prevalence of dental caries was 306(36.3%).The educational status of children's father (AOR=0.3, 95%CI, 0.17, 0.80), monthly household income (AOR=0.59, 95%CI, 0.01, 0.45), regular teeth brushing (AOR=0.08, 95% CI, 0.03, 0.20) and using mouth rinsing (AOR=0.40, 95% CI, 0.2, 0.80) were found statistically significantly associated with dental caries. CONCLUSIONS: Dental caries were high among children in Gondar town. Low socioeconomic status and poor oral hygiene practices were the influencing factors for dental caries. Oral hygiene, dietary habits and access to dental care services are supreme important for the prevention of the problem.

Breast Carcinoma in a 7-Years- Old Girl

This is a case report of a 7 years old female patient diagnosed to have secretory carcinoma of the breast and secondary axillary lymph nodes metastasis after she presented with compliant of left breast swelling that lasted for about 6 months. It is a rare ( 1) type of breast carcinoma with distinct histologic features. Diagnosis of this carcinoma at fine needle aspiration cytology (FNAC) is quite difficult and it is not a particularly aggressive tumor with excellent prognosis even in the presence of metastasis. Axillary locoregional lymph node metastases are uncommon. Several authors; therefore; recommend a conservative and non-aggressive treatment as much as possible. In her case; modified radical mastectomy with level II axillary dissection was done without hormonal or chemotherapy. So far; the therapeutic approach tends to be fairly flexible

Kinetics of DNA load predict HPV 16 viral clearance.

INTRODUCTION: While high HPV 16 viral load measured at a single time point is associated with cervical disease outcomes, few studies have assessed changes in HPV 16 viral load on viral clearance. OBJECTIVE: To measure the association between changes in HPV 16 viral load and viral clearance in a cohort of Thai women infected with HPV 16. STUDY DESIGN: Fifty women (n=50) between the ages of 18-35 years enrolled in a prospective cohort study were followed up every three months for two years. Women positive for HPV 16 DNA by multiplex TaqMan assay at two or more study visits were selected for viral load quantitation using a type-specific TaqMan based real-time PCR assay. The strength of the association of change in viral load between two visits and viral clearance at the subsequent visit was assessed using a GEE model for binary outcomes. RESULTS: At study entry, HPV 16 viral load did not vary by infection outcome. A >2 log decline in viral load across two study visits was found to be strongly associated with viral clearance (AOR: 5.5, 95% CI: 1.4-21.3). HPV 16 viral load measured at a single time point was not associated with viral clearance. CONCLUSIONS: These results demonstrate that repeated measurement of HPV 16 viral load may be a useful predictor in determining the outcome of early endpoints of viral infection.