ABSTRACT
More than 500 diffuse interstellar bands (DIBs) have been observed in astronomical spectra, and their signatures and correlations in different environments have been studied over the past ...decades to reveal clues about the nature of the carriers. We compare the equivalent widths of the DIBs, normalized to the amount of reddening, EB-V, to search for anticorrelated DIB pairs using a data sample containing 54 DIBs measured in 25 sightlines. This data sample covers most of the strong and commonly detected DIBs in the optical region, and the sightlines probe a variety of interstellar medium conditions. We find that 12.9 per cent of the DIB pairs are anticorrelated, and the lowest Pearson correlation coefficient is rnorm ∼ −0.7. We revisit correlation-based DIB families and are able to reproduce the assignments of such families for the well-studied DIBs by applying hierarchical agglomerative and k-means clustering algorithms. We visualize the dissimilarities between DIBs, represented by 1 − rnorm, using multidimensional scaling (MDS). With this representation, we find that the DIBs form a rather continuous sequence, which implies that some properties of the DIB carriers are changing gradually following this sequence. We also find that at that least two factors are needed to properly explain the dissimilarities between DIBs. While the first factor may be interpreted as related to the ionization properties of the DIB carriers, a physical interpretation of the second factor is less clear and may be related to how DIB carriers interact with surrounding interstellar material.
Open tibial shaft fractures are an important source of disability in Latin America. High-income countries (HICs) worldwide have established standardized treatment protocols for open tibial fractures, ...but less is known about their treatment in middle-income countries (MICs) in Latin America. This survey of Latin American orthopaedic surgeons characterizes open tibial fracture treatment patterns.
Orthopaedic surgeons from 20 national orthopaedic societies throughout Latin America completed an online survey assessing their treatment of open tibial fractures. Demographic information was collected. Treatment patterns were queried according to 2 groupings of Gustilo-Anderson (GA) fracture types: treatment of type-I and type-II fractures (GA-I/II) and treatment of type-III fractures (GA-III). Treatment patterns were evaluated across 4 domains: antibiotic prophylaxis, irrigation and debridement, fracture stabilization, and wound management. Summary statistics were reported; analysis was performed using the Fisher exact test (p < 0.05).
There were 616 survey participants from 20 Latin American countries (4 HICs and 16 MICs). Initial external fixation followed by staged internal fixation was preferred for GA-I/II (51.0%) and GA-III fractures (86.0%). Nearly one-third (31.5%) of GA-IIIB fractures did not receive a soft-tissue coverage procedure. Stratifying by country socioeconomic status, surgeons in MICs more commonly utilized delayed internal fixation for GA-I/II (53.3% versus 22.0%, p < 0.001) and GA-III fractures (94.0% versus 80.4%, p = 0.002). Surgeons in MICs more commonly used primary closure for GA-I/II (88.9% versus 62.8%, p < 0.001) and GA-III fractures (32.6% versus 9.8%, p < 0.001).
This survey reports Latin American orthopaedic surgeons' treatment patterns for open tibial shaft fractures. Surgeons in MICs reported higher delayed internal fixation use for all fracture types, while surgeons in HICs more routinely avoid primary closure. Soft-tissue coverage procedures are not performed in nearly one-third of GA-IIIB fractures because of a lack of operative personnel and training.
We present the results of a measurement of isotopic concentrations and atomic number ratio of a double-sided actinide target using α-spectroscopy and mass spectrometry. The double-sided actinide ...target, with predominantly 239Pu on one side and 235U on the other, was used in the fission Time Projection Chamber (fissionTPC) for a measurement of the neutron-induced fission cross-section ratio between the two isotopes. The measured atomic number ratio is needed to extract an absolute measurement fission cross-section ratio. The 239Pu/235U atom number ratio was measured with a combination of mass spectrometry and α-spectroscopy with a planar silicon detector achieving uncertainties of less than 1%. Different strategies for estimating isotopic concentration from the α-spectrum are presented to demonstrate the potential of these methods for non-destructive target assay. We found that a combination of fitting spectra with constraints from mass spectrometry, and summing counts in a region of the spectrum provided the most consistent results with the lowest uncertainty.
All undergraduates in physics and astronomy should have access to significant research experiences. When given the opportunity to tackle challenging open-ended problems outside the classroom, ...students build their problem-solving skills in ways that better prepare them for the workplace or future research in graduate school. Accelerator-based research on fundamental nuclear and particle physics can provide a myriad of opportunities for undergraduate involvement in hardware and software development as well as “big data” analysis. The collaborative nature of large experiments exposes students to scientists of every culture and helps them begin to build their professional network even before they graduate. This paper presents an overview of my experiences - the good, the bad, and the ugly - engaging undergraduates in particle and nuclear physics research at the CERN Large Hadron Collider and the Los Alamos Neutron Science Center.
The fission Time Projection Chamber (fissionTPC) is a compact (15cm diameter) two-chamber MICROMEGAS TPC designed to make precision cross-section measurements of neutron-induced fission. The actinide ...targets are placed on the central cathode and irradiated with a neutron beam that passes axially through the TPC inducing fission in the target. The 4π acceptance for fission fragments and complete charged particle track reconstruction are powerful features of the fissionTPC which will be used to measure fission cross-sections and examine the associated systematic errors. This paper provides a detailed description of the design requirements, the design solutions, and the initial performance of the fissionTPC.
We present the behavior of the cost-effective Planacon MCP-PMTs with 25μm pore diameter in the presence of axial magnetic fields up to 0.5 T. Having a batch of 62 devices of the same type, two ...MCP-PMTs were selected and their gain variation measured in different magnetic fields. These two otherwise identical devices satisfied the selection criteria by requiring the lowest (1.15 kV) and one of the highest (1.4 kV) bias voltage values to achieve a given gain. Both MCP-PMTs have a nearly identical tolerance of the strong magnetic field despite the significant difference in the bias voltage. This clarifies the mechanism of the B-field influence on the MCP-PMT gain, emphasizing the importance of the intrinsic parameters of the MCP emissive coating rather than external parameters, such as the total bias voltage. By evaluating the dependence of both gain and timing parameters on the magnetic field strength, we confirm the operability of such MCP-PMTs in strong magnetic fields in spite of the relatively large pore diameter and low bias voltage required for a given gain.
The EDIBLES survey Fan, Haoyu; Rocha, Carlos M. R.; Cordiner, Martin ...
Astronomy and astrophysics (Berlin),
1/2024, Letnik:
681
Journal Article
Recenzirano
Context.
Small linear carbon chain radicals such as C
2
and C
3
act as both the building blocks and dissociation fragments of larger carbonaceous species. Their rotational excitation traces the ...temperature and density of local environments. However, these homo-nuclear di- and triatomic species are only accessible through their electronic and vibrational features because they lack a permanent dipole moment, and high signal-to-noise ratio data are necessary as the result of their generally low abundances in the interstellar medium (ISM).
Aims.
In order to improve our understanding of small carbonaceous species in the ISM, we carried out a sensitive survey of C
2
and C
3
using the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) dataset. We also expanded our searches to C
4
, C
5
, and the
13
C
12
C isotopologue in the most molecule-rich sightlines.
Methods.
We fitted synthetic spectra generated following a physical excitation model to the C
2
(2-0) Phillips band to obtain the C
2
column density (
N
) as well as the kinetic temperature (
T
kin
) and number density (
n
) of the host cloud. The C
3
molecule was measured through its à − $ \tilde X$ (000-000) electronic origin band system. We simulated the excitation of this band with a double-temperature Boltzmann distribution.
Results.
We present the largest combined survey of C
2
and C
3
to date in which the individual transitions can be resolved. In total, we detected C
2
in 51 velocity components along 40 sightlines, and C
3
in 31 velocity components along 27 sightlines. Further analysis confirms the two molecules are detected in the same velocity components. We find a very good correlation between
N
(C
2
) and
N
(C
3
) with a Pearson correlation coefficient
r
= 0.93 and an average
N
(C
2
)/
N
(C
3
) ratio of 15.5± 1.4. A comparison with the behaviour of the C
2
diffuse interstellar bands (DIBs) shows that there are no clear differences among sightlines with and without detections of C
2
and C
3
. This is in direct contrast to the better-studied non-C
2
DIBs, which have reduced strengths in molecule-rich environments, consistent with the idea that the C
2
DIBs are indeed a distinguishable DIB family. We also identify, for the first time, the
Q
(2),
Q
(3), and
Q
(4) transitions of the
13
C
12
C (2-0) Phillips band in the stacked average spectrum of molecule-rich sightlines, and estimate the isotopic ratio of carbon
12
C/
13
C to be 79±8, consistent with literature results. At this stage it is not yet possible to identify these transitions in individual sightlines. Our search for the C
4
and C
5
optical bands was unsuccessful; even in stacked spectra no unambiguous identification could be made.
Performance of a MICROMEGAS-based TPC in a high-energy neutron beam Snyder, L.; Manning, B.; Bowden, N.S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2018, Letnik:
881
Journal Article
Recenzirano
Odprti dostop
The MICROMEGAS (MICRO-MEsh GAseous Structure) charge amplification structure has found wide use in many detection applications, especially as a gain stage for the charge readout of Time Projection ...Chambers (TPCs). Here we report on the behavior of a MICROMEGAS TPC when operated in a high-energy (up to 800MeV) neutron beam. It is found that neutron-induced reactions can cause discharges in some drift gas mixtures that are stable in the absence of the neutron beam. The discharges result from recoil ions close to the MICROMEGAS that deposit high specific ionization density and have a limited diffusion time. For a binary drift gas, increasing the percentage of the molecular component (quench gas) relative to the noble component and operating at lower pressures generally improves stability.
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