Probing the dynamics of an optically trapped particle by phase sensitive back focal plane interferometry

The dynamics of an optically trapped particle are often determined by measuring intensity shifts of the back-scattered light from the particle using position sensitive detectors. We present a technique which measures the phase of the back-scattered light using balanced detection in an external Mach-Zender interferometer scheme where we separate out and beat the scattered light from the bead and that from the top surface of our trapping chamber. The technique has improved axial motion resolution over intensity-based detection, and can also be used to measure lateral motion of the trapped particle. In addition, we are able to track the Brownian motion of trapped 1 and 3 $\mu$m diameter beads from the phase jitter and show that, similar to intensity-based measurements, phase measurements can also be used to simultaneously determine displacements of the trapped bead as well as the spring constant of the trap. For lateral displacements, we have matched our experimental results with a simulation of the overall phase contour of the back-scattered light for lateral displacements by using plane wave decomposition in conjunction with Mie scattering theory. The position resolution is limited by path drifts of the interferometer which we have presently reduced to obtain a displacement resolution of around 2 nm for 1.1 $\mu$m diameter probes by locking the interferometer to a frequency stabilized diode laser.Comment: 10 pages, 7 figure

Feedback control of particle morphology enables continuous monoclonal antibody capture via precipitation

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Chronostratigraphy of the Larsen blue-ice area in northern Victoria Land, East Antarctica, and its implications for paleoclimate

In blue-ice areas (BIAs), deep ice is directly exposed at the surface, allowing for the cost-effective collection of large-sized old-ice samples. However, chronostratigraphic studies on blue-ice areas are challenging owing to fold and fault structures. Here, we report on a surface transect of ice with an undisturbed horizontal stratigraphy from the Larsen BIA, northern Victoria Land, East Antarctica. Ice layers defined by dust bands and ground-penetrating radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, which result from a complicated fold structure. Stable water isotopes (δ18Oice and δ2Hice) and components of the occluded air (i.e., CO2, N2O, CH4, δ15N–N2, δ18Oatm (=δ18O-O2), δO2/N2, δAr/N2​​​​​​​, 81Kr, and 85Kr) are analyzed for surface ice and shallow ice core samples. Correlating δ18Oice, δ18Oatm, and CH4 records from the Larsen BIA with ice from previously drilled ice cores indicates that the gas age at various shallow vertical coring sites ranges between 9.2–23.4 kyr BP, while the ice age sampled from the surface ranges from 5.6 to 24.7 kyr BP. Absolute radiometric 81Kr dating for the two vertical cores confirms ages within acceptable levels of analytical uncertainty. A tentative climate reconstruction suggests a large deglacial warming of 15 ± 5 ∘C (1σ) and an increase in snow accumulation by a factor of 1.7–4.6 (from 24.3 to 10.6 kyr BP). Our study demonstrates that BIAs in northern Victoria Land may help to obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation, although in general climatic interpretation is complicated by the need for upstream flow corrections, evidence for strong surface sublimation during the last glacial period, and potential errors in the estimated gas age–ice age difference.</p

Nutritional Factors and Susceptibility to Arsenic-Caused Skin Lesions in West Bengal, India

There has been widespread speculation about whether nutritional deficiencies increase the susceptibility to arsenic health effects. This is the first study to investigate whether dietary micronutrient and macronutrient intake modulates the well-established human risk of arsenic-induced skin lesions, including alterations in skin pigmentation and keratoses. The study was conducted in West Bengal, India, which along with Bangladesh constitutes the largest population in the world exposed to arsenic from drinking water. In this case–control study design, cases were patients with arsenic-induced skin lesions and had < 500 μg/L arsenic in their drinking water. For each case, an age- and sex-matched control was selected from participants of a 1995–1996 cross-sectional survey, whose drinking water at that time also contained < 500 μg/L arsenic. Nutritional assessment was based on a 24-hr recall for major dietary constituents and a 1-week recall for less common constituents. Modest increases in risk were related to being in the lowest quintiles of intake of animal protein [odds ratio (OR) = 1.94; 95% confidence interval (CI), 1.05–3.59], calcium (OR = 1.89; 95% CI, 1.04–3.43), fiber (OR = 2.20; 95% CI, 1.15–4.21), and folate (OR = 1.67; 95% CI, 0.87–3.2). Conditional logistic regression suggested that the strongest associations were with low calcium, low animal protein, low folate, and low fiber intake. Nutrient intake was not related to arsenic exposure. We conclude that low intake of calcium, animal protein, folate, and fiber may increase susceptibility to arsenic-caused skin lesions. However, in light of the small magnitude of increased risks related to these dietary deficiencies, prevention should focus on reducing exposure to arsenic

An analysis and evaluation of the WeFold collaborative for protein structure prediction and its pipelines in CASP11 and CASP12

Every two years groups worldwide participate in the Critical Assessment of Protein Structure Prediction (CASP) experiment to blindly test the strengths and weaknesses of their computational methods. CASP has significantly advanced the field but many hurdles still remain, which may require new ideas and collaborations. In 2012 a web-based effort called WeFold, was initiated to promote collaboration within the CASP community and attract researchers from other fields to contribute new ideas to CASP. Members of the WeFold coopetition (cooperation and competition) participated in CASP as individual teams, but also shared components of their methods to create hybrid pipelines and actively contributed to this effort. We assert that the scale and diversity of integrative prediction pipelines could not have been achieved by any individual lab or even by any collaboration among a few partners. The models contributed by the participating groups and generated by the pipelines are publicly available at the WeFold website providing a wealth of data that remains to be tapped. Here, we analyze the results of the 2014 and 2016 pipelines showing improvements according to the CASP assessment as well as areas that require further adjustments and research

An analysis and evaluation of the WeFold collaborative for protein structure prediction and its pipelines in CASP11 and CASP12

Every two years groups worldwide participate in the Critical Assessment of Protein Structure Prediction (CASP) experiment to blindly test the strengths and weaknesses of their computational methods. CASP has significantly advanced the field but many hurdles still remain, which may require new ideas and collaborations. In 2012 a web-based effort called WeFold, was initiated to promote collaboration within the CASP community and attract researchers from other fields to contribute new ideas to CASP. Members of the WeFold coopetition (cooperation and competition) participated in CASP as individual teams, but also shared components of their methods to create hybrid pipelines and actively contributed to this effort. We assert that the scale and diversity of integrative prediction pipelines could not have been achieved by any individual lab or even by any collaboration among a few partners. The models contributed by the participating groups and generated by the pipelines are publicly available at the WeFold website providing a wealth of data that remains to be tapped. Here, we analyze the results of the 2014 and 2016 pipelines showing improvements according to the CASP assessment as well as areas that require further adjustments and research

International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways.

Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined<5 × 10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist

Manipulation de parois de domaine dans les nitrures ferrimagnétiques anti-pérovskites

The boundaries between magnetic domains are known as domain walls (DW). The motion of these DWs using magnetic fields or spin polarized currents has been one of the main focus of spintronics research in the last two decades. One mechanism leading to current induced domain wall motion is the spin transfer torque, where the spin polarized current is generated within the ferromagnetic layer and exerts a torque on the local magnetic moments of the domain walls. The other mechanism is the spin orbit torque, which is now widely used for the domain wall motion experiments, and where the spin polarized current is generated by an adjacent heavy metal layer.Recently, current-induced magnetization dynamics in ferrimagnets has become an active field of research. The magnetic and/or the angular momentum compensation can be achieved by either changing the temperature or by changing the composition of the materials. As the magnetization or the angular momentum that has to be reversed is small close to these points, previous reports on ferrimagnets have evidenced large domain wall velocities under action of spin orbit torques. In this manuscript we will focus on current-driven domain wall dynamics in an epitaxial rare-earth free ferrimagnetic nitride, Manganese Nitride (Mn4N), using spin transfer torques.We show that epitaxially grown Mn4N thin films grown on SrTiO3 substrate have a very low magnetization and mm-scale domains with very low pinning. On this system, DW motion was studied by fabricating nanowires by e-beam lithography. Using magneto optic kerr measurements, we measured a high domain wall velocity of more than 900 m/s in Mn4N at J = 1.3 TA/sq.m, at room temperature, with only spin transfer torque.In order to reach the compensation point, different samples were grown epitaxially while increasing the doping Ni concentration. X-ray magnetic circular dichroism (XMCD) measurements showed that the Ni atoms preferentially occupy the corner site in Mn4N. Since the magnetic moment carried by the Ni atoms is anti-parallel to that of Mn corner atoms , increasing the Ni content decreases the net magnetic moment. Beyond a critical Ni concentration, the net magnetization is then expected to be reversed. Using the values from neutron diffraction measurements, the expected magnetic compensation point lies around Ni atomic concentration of x = 0.18 which corresponds to 3.6% of Ni. The presence of the magnetic compensation point around this concentration is confirmed by XMCD and Anomalous Hall effect measurements. The DW velocity is found to increase as the Ni concentration gets closer to the angular momentum compensation point, with a velocity up to 2000 m/s before the compensation point and approaching 3000 m/s after crossing the compensation point. Interestingly it was also observed that the DW motion direction is reversed beyond the compensation point. In order to explain these results, we used the q–ϕ model, expanded to a ferrimagnetic system consisting of two sub-lattices, and using effective magnetic parameters for the two sub-lattices. If one assumes that the spin polarization does not change after the angular momentum compensation point, the DW motion reversal is therefore due to a relative change of orientation of the net spin polarization with respect to global magnetization.To confirm the validity of these assumptions, ab-initio calculations were performed, showing that the net magnetization is reversed at the Ni concentration x = 0.15, which match well with our experimental results. The simulations confirms that the conduction occurs through the Mn face centered sites, and that the spin polarization remains in the same direction (given by corner sites) while the net magnetization direction is reversed.The studied materials, composed of abundant elements, and free of critical elements such as rare-earths and heavy metals, are thus promising candidates for sustainable spintronics applications.Les frontières entre les domaines magnétiques sont appelées parois de domaine (DW). Le mouvement de ces parois à l'aide de champs magnétiques ou de courants polarisés en spin a été l'un des principaux axes de recherche en spintronique des deux dernières décennies. Un mécanisme conduisant au mouvement de paroi sous courant est le couple de transfert de spin, où le courant polarisé en spin est généré dans la couche ferromagnétique. L'autre mécanisme est le couple spin-orbite, aujourd’hui largement utilisé, et où le courant polarisé en spin est généré par une couche adjacente de matériau spin-orbite. Récemment, le contrôle de l'aimantation par injection de courant dans les matériaux ferrimagnétiques est devenu un important domaine de recherche. La compensation magnétique et/ou de moment cinétique peut être obtenue en modifiant la température ou en modifiant la composition des matériaux. Comme l'aimantation qui doit être renversée est faible près de ces points, des études récentes ont mis en évidence de grandes vitesses de DW sous l'action de couples spin-orbite. Dans ce manuscrit, nous traitons de la propagation des parois de domaine sous l’effet d’un couple de transfert de spin dans un nitrure ferrimagnétique épitaxié, le nitrure de manganèse (Mn4N).Nous montrons que les couches minces de Mn4N développées par épitaxie sur un substrat de SrTiO3 ont une très faible aimantation, et des domaines à l'échelle millimétrique avec un ancrage très faible. Dans ce système, le mouvement des parois de domaine a été étudié en fabriquant des nanofils par lithographie. En utilisant des mesures d’effet Kerr magnéto-optiques, nous avons mesuré des vitesses de paroi de plus de 900 m/s dans Mn4N à J = 1.3 TA/sq.m, à température ambiante, et avec seulement un couple de transfert de spin.Afin d'atteindre le point de compensation, différents échantillons ont été épitaxiés par substitution de Ni. Des mesures de dichroïsme circulaire magnétique aux rayons X(XMCD) ont montré que les atomes de Ni occupent préférentiellement le site du coin à Mn4N. Puisque le moment magnétique porté par les atomes de Ni est anti-parallèle à celui des Mn de coin, l'augmentation de la teneur en Ni diminue le moment magnétique net. Au-delà d'une concentration critique en Ni, l'aimantation nette devrait alors s'inverser. En utilisant les valeurs des mesures de diffraction des neutrons, le point de compensation magnétique attendu se situe autour de 3.6 % de Ni. La présence du point de compensation magnétique autour de cette concentration est confirmée par des mesures de XMCD et d'effet Hall anormal. Les vitesses de la paroi augmentent à mesure que la concentration de Ni se rapproche du point de compensation, avec une vitesse atteignant 2000 m/s avant le point de compensation et approchant 3000 m/s après avoir traversé le point de compensation. Nous avons également observé une inversion de la direction du mouvement de la paroi au-delà du point de compensation. Afin d'expliquer ces résultats, nous avons utilisé le modèle q – ϕ. Si l'on suppose que la polarisation de spin ne change pas après le point de compensation du moment cinétique, l'inversion du mouvement de la paroi du domaine est due à un changement relatif d'orientation de la polarisation de spin nette par rapport à l'aimantation globale. Pour confirmer la validité de ces hypothèses, des calculs ab-initio ont été effectués, montrant que l'aimantation nette est inversée à la concentration de Ni x = 0.15, ce qui correspond bien à nos résultats expérimentaux. Les simulations confirment que la conduction électrique à lieu principalement sur les atomes de centres de faces , et qu’à la transition la polarisation du spin reste dans la même direction alors que la direction de l'aimantation nette est inversée. Les matériaux étudiés, composés d'éléments abondants, et exempts d'éléments critiques comme les terres rares et les métaux lourds, sont ainsi des candidats prometteurs pour des applications de spintronique durable

Manipulation de parois de domaine dans les nitrures ferrimagnétiques anti-pérovskites

The boundaries between magnetic domains are known as domain walls (DW). The motion of these DWs using magnetic fields or spin polarized currents has been one of the main focus of spintronics research in the last two decades. One mechanism leading to current induced domain wall motion is the spin transfer torque, where the spin polarized current is generated within the ferromagnetic layer and exerts a torque on the local magnetic moments of the domain walls. The other mechanism is the spin orbit torque, which is now widely used for the domain wall motion experiments, and where the spin polarized current is generated by an adjacent heavy metal layer.Recently, current-induced magnetization dynamics in ferrimagnets has become an active field of research. The magnetic and/or the angular momentum compensation can be achieved by either changing the temperature or by changing the composition of the materials. As the magnetization or the angular momentum that has to be reversed is small close to these points, previous reports on ferrimagnets have evidenced large domain wall velocities under action of spin orbit torques. In this manuscript we will focus on current-driven domain wall dynamics in an epitaxial rare-earth free ferrimagnetic nitride, Manganese Nitride (Mn4N), using spin transfer torques.We show that epitaxially grown Mn4N thin films grown on SrTiO3 substrate have a very low magnetization and mm-scale domains with very low pinning. On this system, DW motion was studied by fabricating nanowires by e-beam lithography. Using magneto optic kerr measurements, we measured a high domain wall velocity of more than 900 m/s in Mn4N at J = 1.3 TA/sq.m, at room temperature, with only spin transfer torque.In order to reach the compensation point, different samples were grown epitaxially while increasing the doping Ni concentration. X-ray magnetic circular dichroism (XMCD) measurements showed that the Ni atoms preferentially occupy the corner site in Mn4N. Since the magnetic moment carried by the Ni atoms is anti-parallel to that of Mn corner atoms , increasing the Ni content decreases the net magnetic moment. Beyond a critical Ni concentration, the net magnetization is then expected to be reversed. Using the values from neutron diffraction measurements, the expected magnetic compensation point lies around Ni atomic concentration of x = 0.18 which corresponds to 3.6% of Ni. The presence of the magnetic compensation point around this concentration is confirmed by XMCD and Anomalous Hall effect measurements. The DW velocity is found to increase as the Ni concentration gets closer to the angular momentum compensation point, with a velocity up to 2000 m/s before the compensation point and approaching 3000 m/s after crossing the compensation point. Interestingly it was also observed that the DW motion direction is reversed beyond the compensation point. In order to explain these results, we used the q–ϕ model, expanded to a ferrimagnetic system consisting of two sub-lattices, and using effective magnetic parameters for the two sub-lattices. If one assumes that the spin polarization does not change after the angular momentum compensation point, the DW motion reversal is therefore due to a relative change of orientation of the net spin polarization with respect to global magnetization.To confirm the validity of these assumptions, ab-initio calculations were performed, showing that the net magnetization is reversed at the Ni concentration x = 0.15, which match well with our experimental results. The simulations confirms that the conduction occurs through the Mn face centered sites, and that the spin polarization remains in the same direction (given by corner sites) while the net magnetization direction is reversed.The studied materials, composed of abundant elements, and free of critical elements such as rare-earths and heavy metals, are thus promising candidates for sustainable spintronics applications.Les frontières entre les domaines magnétiques sont appelées parois de domaine (DW). Le mouvement de ces parois à l'aide de champs magnétiques ou de courants polarisés en spin a été l'un des principaux axes de recherche en spintronique des deux dernières décennies. Un mécanisme conduisant au mouvement de paroi sous courant est le couple de transfert de spin, où le courant polarisé en spin est généré dans la couche ferromagnétique. L'autre mécanisme est le couple spin-orbite, aujourd’hui largement utilisé, et où le courant polarisé en spin est généré par une couche adjacente de matériau spin-orbite. Récemment, le contrôle de l'aimantation par injection de courant dans les matériaux ferrimagnétiques est devenu un important domaine de recherche. La compensation magnétique et/ou de moment cinétique peut être obtenue en modifiant la température ou en modifiant la composition des matériaux. Comme l'aimantation qui doit être renversée est faible près de ces points, des études récentes ont mis en évidence de grandes vitesses de DW sous l'action de couples spin-orbite. Dans ce manuscrit, nous traitons de la propagation des parois de domaine sous l’effet d’un couple de transfert de spin dans un nitrure ferrimagnétique épitaxié, le nitrure de manganèse (Mn4N).Nous montrons que les couches minces de Mn4N développées par épitaxie sur un substrat de SrTiO3 ont une très faible aimantation, et des domaines à l'échelle millimétrique avec un ancrage très faible. Dans ce système, le mouvement des parois de domaine a été étudié en fabriquant des nanofils par lithographie. En utilisant des mesures d’effet Kerr magnéto-optiques, nous avons mesuré des vitesses de paroi de plus de 900 m/s dans Mn4N à J = 1.3 TA/sq.m, à température ambiante, et avec seulement un couple de transfert de spin.Afin d'atteindre le point de compensation, différents échantillons ont été épitaxiés par substitution de Ni. Des mesures de dichroïsme circulaire magnétique aux rayons X(XMCD) ont montré que les atomes de Ni occupent préférentiellement le site du coin à Mn4N. Puisque le moment magnétique porté par les atomes de Ni est anti-parallèle à celui des Mn de coin, l'augmentation de la teneur en Ni diminue le moment magnétique net. Au-delà d'une concentration critique en Ni, l'aimantation nette devrait alors s'inverser. En utilisant les valeurs des mesures de diffraction des neutrons, le point de compensation magnétique attendu se situe autour de 3.6 % de Ni. La présence du point de compensation magnétique autour de cette concentration est confirmée par des mesures de XMCD et d'effet Hall anormal. Les vitesses de la paroi augmentent à mesure que la concentration de Ni se rapproche du point de compensation, avec une vitesse atteignant 2000 m/s avant le point de compensation et approchant 3000 m/s après avoir traversé le point de compensation. Nous avons également observé une inversion de la direction du mouvement de la paroi au-delà du point de compensation. Afin d'expliquer ces résultats, nous avons utilisé le modèle q – ϕ. Si l'on suppose que la polarisation de spin ne change pas après le point de compensation du moment cinétique, l'inversion du mouvement de la paroi du domaine est due à un changement relatif d'orientation de la polarisation de spin nette par rapport à l'aimantation globale. Pour confirmer la validité de ces hypothèses, des calculs ab-initio ont été effectués, montrant que l'aimantation nette est inversée à la concentration de Ni x = 0.15, ce qui correspond bien à nos résultats expérimentaux. Les simulations confirment que la conduction électrique à lieu principalement sur les atomes de centres de faces , et qu’à la transition la polarisation du spin reste dans la même direction alors que la direction de l'aimantation nette est inversée. Les matériaux étudiés, composés d'éléments abondants, et exempts d'éléments critiques comme les terres rares et les métaux lourds, sont ainsi des candidats prometteurs pour des applications de spintronique durable