81 research outputs found
Demonstration of an optical polarization magnifier with low birefringence
In any polarimetric measurement technique, enhancing the laser polarization
change of a laser beam before it reaches the analyzer can help in improving the
sensitivity. This can be performed using an optical component having a large
linear dichroism, the enhancement factor being equal to the square root of the
ratio of the two transmission factors. A pile of parallel plates at Brewster
incidence looks appropriate for realizing such a polarization magnifier. In
this paper, we address the problem raised by the interference in the plates and
between the plates, which affects the measurement by giving rise to
birefringence. We demonstrate that wedged plates provide a convenient and
efficient way to avoid this interference. We have implemented and characterized
devices with 4 and 6 wedged plates at Brewster incidence which have led to a
decisive improvement of the signal to noise ratio in our ongoing Parity
Violation measurement.Comment: 08 october 200
A new Manifestation of Atomic Parity Violation in Cesium: a Chiral Optical Gain induced by linearly polarized 6S-7S Excitation
We have detected, by using stimulated emission, an Atomic Parity Violation
(APV) in the form of a chiral optical gain of a cesium vapor on the 7S -
6P transition,consecutive to linearly polarized 6S-7S excitation. We
demonstrate the validity of this detection method of APV, by presenting a 9%
accurate measurement of expected sign and magnitude. We underline several
advantages of this entirely new approach in which the cylindrical symmetry of
the set-up can be fully exploited. Future measurements at the percent level
will provide an important cross-check of an existing more precise result
obtained by a different method.Comment: 4 pages, 2 figure
Atomic Parity Violation : Principles, Recent Results, Present Motivations
We review the progress made in the determination of the weak charge, Q\_w, of
the cesium nucleus which raises the status of Atomic Parity Violation
measurements to that of a precision electroweak test. Not only is it necessary
to have a precision measurement of the electroweak asymmetry in the highly
forbidden 6S-7S transition, but one also needs a precise calibration procedure.
The 1999 precision measurement by the Boulder group implied a 2.5 sigma
deviation of Q\_w from the theoretical prediction. This triggered many particle
physicist suggestions as well as examination by atomic theoretical physicists
of several sources of corrections. After about three years the disagreement was
removed without appealing to "New Physics". Concurrently, an original
experimental approach was developed in our group for more than a decade. It is
based on detection by stimulated emission with amplification of the left- right
asymmetry. We present our decisive, recent progress together with our latest
results. We emphasize the important impact for electroweak theory, of future
measurements in cesium possibly pushed to the 0.1% level. Other possible
approaches are currently explored in several atoms
Osteochondral transplantation using autografts from the upper tibio-fibular joint for the treatment of knee cartilage lesions
Purpose Treatment of large cartilage lesions of the knee
in weight-bearing areas is still a controversy and challenging topic. Autologous osteochondral mosaicplasty has
proven to be a valid option for treatment but donor site
morbidity with most frequently used autografts remains a
source of concern. This study aims to assess clinical results
and safety profile of autologous osteochondral graft from
the upper tibio-fibular joint applied to reconstruct symptomatic osteochondral lesions of the knee.
Methods Thirty-one patients (22 men and 9 women) with
grade 4 cartilage lesions in the knee were operated by
mosaicplasty technique using autologous osteochondral
graft from the upper tibio-fibular joint, between 1998 and
2006. Clinical assessment included visual analog scale
(VAS) for pain and Lysholm score. All patients were
evaluated by MRI pre- and post-operatively regarding joint
congruency as good, fair (inferior to 1 mm incongruence),
and poor (incongruence higher than 1 mm registered in any
frame). Donor zone status was evaluated according to
specific protocol considering upper tibio-fibular joint
instability, pain, neurological complications, lateral collateral ligament insufficiency, or ankle complaints.
Results Mean age at surgery was 30.1 years (SD 12.2). In
respect to lesion sites, 22 were located in weight-bearing
area of medial femoral condyle, 7 in lateral femoral condyle, 1 in trochlea, and 1 in patella. Mean follow-up was
110.1 months (SD 23.2). Mean area of lesion was 3.3 cm
2
(SD 1.7), and a variable number of cylinders were used,
mean 2.5 (SD 1.3). Mean VAS score improved from 47.1
(SD 10.1) to 20.0 (SD 11.5); p = 0.00. Similarly, mean
Lysholm score increased from 45.7 (SD 4.5) to 85.3
(SD 7.0); p = 0.00. The level of patient satisfaction was
evaluated, and 28 patients declared to be satisfied/very
satisfied and would do surgery again, while 3 declared as
unsatisfied with the procedure and would not submit to
surgery again. These three patients had lower clinical scores
and kept complaints related to the original problem but
unrelated to donor zone. MRI score significantly improved
at 18–24 months comparing with pre-operative (p = 0.004).
No radiographic or clinical complications related to donor
zone with implication in activity were registered.
Conclusions This work corroborates that mosaicplasty
technique using autologous osteochondral graft from the
upper tibio-fibular joint is effective to treat osteochondral
defects in the knee joint. No relevant complications related
to donor zone were registered
Variability in the analysis of a single neuroimaging dataset by many teams
Data analysis workflows in many scientific domains have become increasingly complex and flexible. To assess the impact of this flexibility on functional magnetic resonance imaging (fMRI) results, the same dataset was independently analyzed by 70 teams, testing nine ex-ante hypotheses. The flexibility of analytic approaches is exemplified by the fact that no two teams chose identical workflows to analyze the data. This flexibility resulted in sizeable variation in hypothesis test results, even for teams whose statistical maps were highly correlated at intermediate stages of their analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Importantly, meta-analytic approaches that aggregated information across teams yielded significant consensus in activated regions across teams. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset. Our findings show that analytic flexibility can have substantial effects on scientific conclusions, and demonstrate factors related to variability in fMRI. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for multiple analyses of the same data. Potential approaches to mitigate issues related to analytical variability are discussed
Variability in the analysis of a single neuroimaging dataset by many teams
Data analysis workflows in many scientific domains have become increasingly complex and flexible. To assess the impact of this flexibility on functional magnetic resonance imaging (fMRI) results, the same dataset was independently analyzed by 70 teams, testing nine ex-ante hypotheses. The flexibility of analytic approaches is exemplified by the fact that no two teams chose identical workflows to analyze the data. This flexibility resulted in sizeable variation in hypothesis test results, even for teams whose statistical maps were highly correlated at intermediate stages of their analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Importantly, meta-analytic approaches that aggregated information across teams yielded significant consensus in activated regions across teams. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset. Our findings show that analytic flexibility can have substantial effects on scientific conclusions, and demonstrate factors related to variability in fMRI. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for multiple analyses of the same data. Potential approaches to mitigate issues related to analytical variability are discussed
Grooving an alumina surface as a means to inhibit secondary electron emission under grazing incidence
A Leak in the Academic Pipeline: Identity and Health Among Postdoctoral Women
Several challenges (e.g., sexism, parental leave, the glass ceiling, etc.) disproportionately affect women in academia (and beyond), and thus perpetuate the leaky pipeline metaphor for women who opt-out of an academic career. Although this pattern can be seen at all levels of the academic hierarchy, a critical time for women facing such challenges is during the postdoctoral stage, when personal life transitions and professional ambitions collide. Using a social identity approach, we explore factors affecting the mental health of postdoctoral women, including identity development (e.g., as a mother, a scientist) and lack of control (uncertainty about one's future personal and professional prospects), which likely contribute to the leak from academia. In this mixed-method research, Study 1 comprised interviews with postdoctoral women in North America (n = 13) and Europe (n = 8) across a range disciplines (e.g., psychology, physics, political science). Common themes included the negative impact of career uncertainty, gender-based challenges (especially sexism and maternity leave), and work-life balance on mental and physical health. However, interviewees also described attempts to overcome gender inequality and institutional barriers by drawing on support networks. Study 2 comprised an online survey of postdoctoral women (N = 146) from a range of countries and academic disciplines to assess the relationships between social identification (e.g., disciplinary, gender, social group), perceived control (i.e., over work and life), and mental health (i.e., depression, anxiety, stress, and life satisfaction). Postdoctoral women showed mild levels of stress and depression, and were only slightly satisfied with life. They also showed only moderate levels of perceived control over one's life and work. However, hierarchical regression analyses revealed that strongly identifying with one's discipline was most consistently positively associated with both perceived control and mental health. Collectively, these findings implicate the postdoctoral stage as being stressful and tenuous for women regardless of academic background or nationality. They also highlight the importance of disciplinary identity as a potentially protective factor for mental health that, in turn, may diminish the rate at which postdoctoral women leak from the academic pipeline
Chromatic bacteria – A broad host-range plasmid and chromosomal insertion toolbox for fluorescent protein expression in bacteria
© 2018 Schlechter, Jun, Bernach, Oso, Boyd, Muñoz-Lintz, Dobson, Remus and Remus-Emsermann. Differential fluorescent labeling of bacteria has become instrumental for many aspects of microbiological research, such as the study of biofilm formation, bacterial individuality, evolution, and bacterial behavior in complex environments. We designed a variety of plasmids, each bearing one of eight unique, constitutively expressed fluorescent protein genes in conjunction with one of four different antibiotic resistance combinations. The fluorophores mTagBFP2, mTurquoise2, sGFP2, mClover3, sYFP2, mOrange2, mScarlet-I, and mCardinal, encoding for blue, cyan, green, green–yellow, yellow, orange, red, and far-red fluorescent proteins, respectively, were combined with selectable markers conferring tetracycline, gentamicin, kanamycin, and/or chloramphenicol resistance. These constructs were cloned into three different plasmid backbones: a broad host-range plasmid, a Tn5 transposon delivery plasmid, and a Tn7 transposon delivery plasmid. The utility of the plasmids and transposons was tested in bacteria from the phyla Actinobacteria, Proteobacteria, and Bacteroidetes. We were able to tag representatives from the phylum Proteobacteria at least via our Tn5 transposon delivery system. The present study enables labeling bacteria with a set of plasmids available to the community. One potential application of fluorescently-tagged bacterial species is the study of bacteria–bacteria, bacteria–host, and bacteria–environment interactions
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