Frozen-Density Embedding

Baerends, E.J. [Promotor]Visscher, L. [Copromotor

Effect of cryopreservation on germination of seeds and zygotic embryos of Calamus shendurunii an endemic rattan of Western Ghats

Calamus shendurunii is an endemic rattan of Western Ghats having restricted distribution and limited population. As a prerequisite to device an appropriate method for ex situ conservation of the species, desiccation and cryopreservation of seeds and zygotic embryo has been studied. Seeds extracted from ripened fruits possessed 35 per cent moisture content and exhibited 97 per cent germination. Desiccation to 28 per cent moisture content reduced the germination to 77 per cent. Desiccation below 14 per cent moisture content caused complete loss of seed germinability. Seeds stored under ambient conditions (28±2oC/60% RH) for more than seven days reduced germination to less than 40 per cent. Thus, conventional storage is not effective for their ex situ conservation. As an alternative method, excised zygotic embryos were subjected to desiccation and storage in liquid nitrogen. The embryos tolerated desiccation down to 5 per cent exhibiting 60 to 90 per cent germination upon culture into MS medium. Desiccated embryos subjected to liquid nitrogen exposure showed post freeze recovery and germination (80-90%) equal to that of desiccated control samples. Thus the study proved the extreme recalcitrance of C. shendurunii seeds and embryo cryopreservation as an alternative method of their ex situ conservation in gene banks

Sodium cationization can disrupt the intramolecular hydrogen bond that mediates the sunscreen activity of oxybenzone

A key decay pathway by which organic sunscreen molecules dissipate harmful UV energy involves excited-state hydrogen atom transfer between proximal enol and keto functional groups. Structural modifications of this molecular architecture have the potential to block ultrafast decay processes, and hence promote direct excited-state molecular dissociation, profoundly affecting the efficiency of an organic sunscreen. Herein, we investigate the binding of alkali metal cations to a prototype organic sunscreen molecule, oxybenzone, using IR characterization. Mass-selective IR action spectroscopy was conducted at the free electron laser for infrared experiments, FELIX (600-1800 cm-1), on complexes of Na+, K+ and Rb+ bound to oxybenzone. The IR spectra reveal that K+ and Rb+ adopt binding positions away from the key OH intermolecular hydrogen bond, while the smaller Na+ cation binds directly between the keto and enol oxygens, thus breaking the intramolecular hydrogen bond. UV laser photodissociation spectroscopy was also performed on the series of complexes, with the Na+ complex displaying a distinctive electronic spectrum compared to those of K+ and Rb+, in line with the IR spectroscopy results. TD-DFT calculations reveal that the origin of the changes in the electronic spectra can be linked to rupture of the intramolecular bond in the sodium cationized complex. The implications of our results for the performance of sunscreens in mixtures and environments with high concentrations of metal cations are discussed

Asymptotic Scaling of the Diffusion Coefficient of Fluctuating "Pulled" Fronts

We present a (heuristic) theoretical derivation for the scaling of the diffusion coefficient $D_f$ for fluctuating ``pulled'' fronts. In agreement with earlier numerical simulations, we find that as $N\to\infty$, $D_f$ approaches zero as $1/\ln^3N$, where $N$ is the average number of particles per correlation volume in the stable phase of the front. This behaviour of $D_f$ stems from the shape fluctuations at the very tip of the front, and is independent of the microscopic model.Comment: Some minor algebra corrected, to appear in Rapid Comm., Phys. Rev.

Sustainability-focused international PBL project:Rethinking digital education for individuals of low socioeconomic status

Providing access to education for individuals of lower socio-economic status is a significant way to reduce poverty, as it empowers them to grow as professionals and as individuals. Although there is an increasing sense of urgency to promote these changes, notably motivated by the Sustainable Development Goals (SDGs) set by the UN 2030 Agenda, there are still few successful ways to solve this problem on a large-scale. As digital technology develops and affordability increases, new ways to share quality educational content are created. In an exploratory case study, with a qualitative approach, this paper presents the development of a digital application focused on providing quality educational content directed to vulnerable groups that lack access to formal learning experiences, specifically focused on waste pickers in Brasilia, Brazil. The main data collection methods used to make the decisions through the development process were observation, surveys, and interviews. Within the framework of Problem Based Learning (PBL) an international cross-disciplinary collaboration among different universities, the project, denominated “Mobile Education”, involved: (i) the design and implementation of a system consisting of both a web and mobile application; (ii) the research of a viable business model to provide long-term sustainability for the project; (iii) and the creation of a pilot course of financial education for the preliminary target group, i.e., waste pickers from Brasilia, Brazil. Conclusively, the project aims to positively impact social transformation for individuals who work at the Waste Sorting facilities and lack financial knowledge. The Mobile Education project resulted in a functional version of the app (Web and Mobile) as well as the delimitation of a viable business model to keep it providing digital equality in Brazilian education

Q2Q^2 Independence of QF2/F1QF_2/F_1, Poincare Invariance and the Non-Conservation of Helicity

A relativistic constituent quark model is found to reproduce the recent data regarding the ratio of proton form factors, $F_2(Q^2)/F_1(Q^2)$. We show that imposing Poincare invariance leads to substantial violation of the helicity conservation rule, as well as an analytic result that the ratio $F_2(Q^2)/F_1(Q^2)\sim 1/Q$ for intermediate values of $Q^2$.Comment: 13 pages, 7 figures, to be submitted to Phys. Rev. C typos corrected, references added, 1 new figure to show very high Q^2 behavio

The Role of Color Neutrality in Nuclear Physics--Modifications of Nucleonic Wave Functions

The influence of the nuclear medium upon the internal structure of a composite nucleon is examined. The interaction with the medium is assumed to depend on the relative distances between the quarks in the nucleon consistent with the notion of color neutrality, and to be proportional to the nucleon density. In the resulting description the nucleon in matter is a superposition of the ground state (free nucleon) and radial excitations. The effects of the nuclear medium on the electromagnetic and weak nucleon form factors, and the nucleon structure function are computed using a light-front constituent quark model. Further experimental consequences are examined by considering the electromagnetic nuclear response functions. The effects of color neutrality supply small but significant corrections to predictions of observables.Comment: 37 pages, postscript figures available on request to [email protected]

Possible origins of macroscopic left-right asymmetry in organisms

I consider the microscopic mechanisms by which a particular left-right (L/R) asymmetry is generated at the organism level from the microscopic handedness of cytoskeletal molecules. In light of a fundamental symmetry principle, the typical pattern-formation mechanisms of diffusion plus regulation cannot implement the "right-hand rule"; at the microscopic level, the cell's cytoskeleton of chiral filaments seems always to be involved, usually in collective states driven by polymerization forces or molecular motors. It seems particularly easy for handedness to emerge in a shear or rotation in the background of an effectively two-dimensional system, such as the cell membrane or a layer of cells, as this requires no pre-existing axis apart from the layer normal. I detail a scenario involving actin/myosin layers in snails and in C. elegans, and also one about the microtubule layer in plant cells. I also survey the other examples that I am aware of, such as the emergence of handedness such as the emergence of handedness in neurons, in eukaryote cell motility, and in non-flagellated bacteria.Comment: 42 pages, 6 figures, resubmitted to J. Stat. Phys. special issue. Major rewrite, rearranged sections/subsections, new Fig 3 + 6, new physics in Sec 2.4 and 3.4.1, added Sec 5 and subsections of Sec

Observations sur la langue dans les lettres adressées a Š. Ljubić

Dans le présent article sont examinées certaines questions portant sur la langue et l\u27orthographe telles qu\u27on peut les constater dans les lettres faisant partie du legs de Š. Ljubić conservé dans les Archives historiques de Zadar. Leur date se situe autour de la moitié du 19e siècle. Les auteurs de ces lettres sont I. Kukuljević Sakcinski, A. Torkvato Brlić, B. Petranović et Š. Starčević. Donc, un Zagrébien, un autre provenant de Slavonie et deux Dalmates, dont l\u27un était Serbe et l\u27autre Croate. De cette manière dans ces lettres sont représentées toutes les couches et structures et les principaux courants de la Croatie avec leurs vues sur la langue littéraire