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The woman who split the atom
\"As a female Jewish physicist in Berlin during the early 20th century, Lise Meitner had to fight for an education, a job, and equal treatment in her field, like having her name listed on her own research papers. Meitner made groundbreaking strides in the study of radiation, but when Hitler came to power in Germany, she suddenly had to face not only sexism, but also life-threatening anti-Semitism as well. Nevertheless, she persevered and one day made a discovery that rocked the world: the splitting of the atom. While her male lab partner was awarded a Nobel Prize for the achievement, the committee refused to give her any credit. Suddenly, the race to build the atomic bomb was on-although Meitner was horrified to be associated with such a weapon. \"A physicist who never lost her humanity,\" Meitner wanted only to figure out how the world works, and advocated for pacifism while others called for war. The book includes an afterword, author's note, timeline, select terms of physics, glossary of scientists mentioned, endnotes, select bibliography, index, and Marissa Moss' celebrated drawings throughout. The Woman Who Split the Atom is a fascinating look at Meitner's fierce passion, integrity, and her life-long struggle to have her contributions to physics recognized\"-- Provided by publisher.
Book
The Drp1-Mediated Mitochondrial Fission Protein Interactome as an Emerging Core Player in Mitochondrial Dynamics and Cardiovascular Disease Therapy
Mitochondria, the membrane-bound cell organelles that supply most of the energy needed for cell function, are highly regulated, dynamic organelles bearing the ability to alter both form and functionality rapidly to maintain normal physiological events and challenge stress to the cell. This amazingly vibrant movement and distribution of mitochondria within cells is controlled by the highly coordinated interplay between mitochondrial dynamic processes and fission and fusion events, as well as mitochondrial quality-control processes, mainly mitochondrial autophagy (also known as mitophagy). Fusion connects and unites neighboring depolarized mitochondria to derive a healthy and distinct mitochondrion. In contrast, fission segregates damaged mitochondria from intact and healthy counterparts and is followed by selective clearance of the damaged mitochondria via mitochondrial specific autophagy, i.e., mitophagy. Hence, the mitochondrial processes encompass all coordinated events of fusion, fission, mitophagy, and biogenesis for sustaining mitochondrial homeostasis. Accumulated evidence strongly suggests that mitochondrial impairment has already emerged as a core player in the pathogenesis, progression, and development of various human diseases, including cardiovascular ailments, the leading causes of death globally, which take an estimated 17.9 million lives each year. The crucial factor governing the fission process is the recruitment of dynamin-related protein 1 (Drp1), a GTPase that regulates mitochondrial fission, from the cytosol to the outer mitochondrial membrane in a guanosine triphosphate (GTP)-dependent manner, where it is oligomerized and self-assembles into spiral structures. In this review, we first aim to describe the structural elements, functionality, and regulatory mechanisms of the key mitochondrial fission protein, Drp1, and other mitochondrial fission adaptor proteins, including mitochondrial fission 1 (Fis1), mitochondrial fission factor (Mff), mitochondrial dynamics 49 (Mid49), and mitochondrial dynamics 51 (Mid51). The core area of the review focuses on the recent advances in understanding the role of the Drp1-mediated mitochondrial fission adaptor protein interactome to unravel the missing links of mitochondrial fission events. Lastly, we discuss the promising mitochondria-targeted therapeutic approaches that involve fission, as well as current evidence on Drp1-mediated fission protein interactions and their critical roles in the pathogeneses of cardiovascular diseases (CVDs).
Journal Article
Constructing, conducting and interpreting animal social network analysis
Animal social networks are descriptions of social structure which, aside from their intrinsic interest for understanding sociality, can have significant bearing across many fields of biology. Network analysis provides a flexible toolbox for testing a broad range of hypotheses, and for describing the social system of species or populations in a quantitative and comparable manner. However, it requires careful consideration of underlying assumptions, in particular differentiating real from observed networks and controlling for inherent biases that are common in social data. We provide a practical guide for using this framework to analyse animal social systems and test hypotheses. First, we discuss key considerations when defining nodes and edges, and when designing methods for collecting data. We discuss different approaches for inferring social networks from these data and displaying them. We then provide an overview of methods for quantifying properties of nodes and networks, as well as for testing hypotheses concerning network structure and network processes. Finally, we provide information about assessing the power and accuracy of an observed network. Alongside this manuscript, we provide appendices containing background information on common programming routines and worked examples of how to perform network analysis using the r programming language. We conclude by discussing some of the major current challenges in social network analysis and interesting future directions. In particular, we highlight the under‐exploited potential of experimental manipulations on social networks to address research questions.
Journal Article
On growth and form of etched fission tracks in apatite; a kinetic approach
We discuss differences between the bulk etch rate (νB) and an alternative radial etch rate (νR) model for fission-track etching in apatite. A skeletal νR-model, based on the inferred orientations of the νR minima and maxima, accounts for the main geometrical features of etched fission tracks, including the track-surface intersections, track channels and their terminations, and the outlines of confined tracks. It unifies the diverse appearances of etched tracks as variations of a basic plan, governed by the orientation of the etched surface and that of the track. The νR-model also embeds fission-track etching in the mainstream theories of crystal growth and dissolution. However, in contrast to the νB-model, the νR-model does not provide bottom-up criteria for discriminating between tracks that are counted by an observer or a computer program and those that are not. Moreover, abandoning the νB-model implies that basic assumptions of fission-track dating must be reconsidered, in particular that track counting efficiencies depend only on a critical dip angle, and are thus independent of the track registration geometry and the length distribution.
Journal Article
Application of the Hill-Wheeler Formula in Statistical Models of Nuclear Fission: A Statistical–Mechanical Approach Based on Similarities with Semiconductor Physics
This study proposes a novel theoretical approach to understanding the statistical–mechanical similarities between nuclear fission phenomena and semiconductor physics. Using the Hill–Wheeler formula as a quantum mechanical distribution function and establishing its correspondence with the Fermi–Dirac distribution function, we analyzed nuclear fission processes for nine nuclides (232Th, 233U, 235U, 238U, 237Np, 239Pu, 240Pu, 242Pu, 241Am) using JENDL-5.0 data.
Journal Article
Exploring Fission Dynamics through Fission Fragment Spectroscopy
Fission Fragment Spectroscopy (FFS) measurement technique has been utilized to measure the relative isotopic yield distributions of the even-even correlated fission fragment nuclei produced from
236
U* at two different values of excitation energies (E
ex
). The fissioning compound nucleus,
236
U* was populated at E
ex
= 6.5 and 21.5 MeV through two different sets of experiments by using the reactions,
235
U(n
th
,
f
) and
232
Th(
α
,
f
), respectively. The experimentally measured relative isotopic yield distributions were further used to obtain the corresponding mass yield distributions. The extracted mass yield distributions of
236
U* indicates the transition from asymmetric distribution to bimodal distribution with increase in the values of E
ex
from 6.5 to 21.5 MeV. The experimental mass yield distribution pattern for the reaction,
232
Th(
α
,
f
) at E
ex
= 21.5 MeV could be fitted well through three Gaussian fits as per the prescription based on the Multimodal Random-Neck Rupture Model (MM-RNRM).
Journal Article
Bonobo optimizer (BO): an intelligent heuristic with self-adjusting parameters over continuous spaces and its applications to engineering problems
In this paper, an intelligent optimization technique, namely Bonobo Optimizer (BO), is proposed. It mimics several interesting reproductive strategies and social behaviour of Bonobos. Bonobos live in a fission-fusion type of social organization, where they form several groups (fission) of different sizes and compositions within the society and move throughout the territory. Afterward, they merge (fusion) again with their society members for conducting specific activities. Bonobos adopt four different reproductive strategies, like restrictive mating, promiscuous mating, extra-group mating, and consortship mating to maintain a proper harmony in the society. These natural strategies are mathematically modeled in the proposed BO to solve an optimization problem. The searching mechanism with self-adjusting controlling parameters of the BO is designed in such a way that it can cope with various situations efficiently, while solving a variety of problems. Moreover, fission-fusion strategy is followed to select the mating partner, which is a unique approach in the literature of meta-heuristics. The performance of BO has been tested on CEC’13 and CEC’14 test functions and compared to that of other efficient and popular optimization algorithms of recent times. The comparisons show some comparable results and statistically superior performances of the proposed BO. Besides these, five complex real-life optimization problems are solved using BO and the results are compared with those reported in the literature. Here also, the performance of BO is found to be either better or comparable than that of others. These results establish the applicability of proposed BO to solve optimization problems.
Journal Article
Quintet-triplet mixing determines the fate of the multiexciton state produced by singlet fission in a terrylenediimide dimer at room temperature
Singlet fission (SF) is a photophysical process in which one of two adjacent organic molecules absorbs a single photon, resulting in rapid formation of a correlated triplet pair (T₁T₁) state whose spin dynamics influence the successful generation of uncorrelated triplets (T₁). Femtosecond transient visible and near-infrared absorption spectroscopy of a linear terrylene-3,4:11,12-bis(dicarboximide) dimer (TDI₂), in which the two TDI molecules are directly linked at one of their imide positions, reveals ultrafast formation of the (T₁T₁) state. The spin dynamics of the (T₁T₁) state and the processes leading to uncoupled triplets (T₁) were studied at room temperature for TDI₂ aligned in 4-cyano-4′-pentylbiphenyl (5CB), a nematic liquid crystal. Time-resolved electron paramagnetic resonance spectroscopy shows that the (T₁T₁) state has mixed ⁵(T₁T₁) and ³(T₁T₁) character at room temperature. This mixing is magnetic field dependent, resulting in a maximum triplet yield at ∼200 mT. The accessibility of the ³(T₁T₁) state opens a pathway for triplet–triplet annihilation that produces a single uncorrelated T₁ state. The presence of the ⁵(T₁T₁) state at room temperature and its relationship with the ¹(T₁T₁) and ³(T₁T₁) states emphasize that understanding the relationship among different (T₁T₁) spin states is critical for ensuring high-yield T₁ formation from singlet fission.
Journal Article
Spatial separation of triplet excitons drives endothermic singlet fission
Molecules that undergo singlet fission, converting singlet excitons into pairs of triplet excitons, have potential as photovoltaic materials. The possible advantages of endothermic singlet fission (enhanced use of photon energy and larger triplet energies for coupling with common absorbers) motivated us to assess the role of exciton delocalization in the activation of this process. Here we report the synthesis of a series of linear perylene oligomers that undergo endothermic singlet fission and have endothermicities in the range 5–10 kBT at room temperature in solution. We study these compounds using transient spectroscopy and modelling to unravel the singlet and triplet dynamics. We show that the minimal number of coupled chromophores needed to undergo endothermic singlet fission is three, which provides sufficient statistical space for triplet excitons to separate and avoid annihilation—and a subsequent fast return to the singlet state. Our data additionally suggest that torsional motion of chromophores about the molecular axis following triplet-pair separation contributes to the increase in entropy, thus lengthening the triplet lifetime in longer oligomers.Generating high-energy triplet excitons from singlet fission without excess energy loss is a critical goal for potential applications. Now it is shown that molecular chromophores that are connected covalently can harbour multiple long-lived and high-energy triplets—created from one photon—only if more than two chromophoric units are present and they have sufficient flexibility to isolate the excitations upon torsional motion.
Journal Article
Membrane fission by protein crowding
Membrane fission, which facilitates compartmentalization of biological processes into discrete, membrane-bound volumes, is essential for cellular life. Proteins with specific structural features including constricting rings, helical scaffolds, and hydrophobic membrane insertions are thought to be the primary drivers of fission. In contrast, here we report a mechanism of fission that is independent of protein structure—steric pressure among membranebound proteins. In particular, random collisions among crowded proteins generate substantial pressure, which if unbalanced on the opposite membrane surface can dramatically increase membrane curvature, leading to fission. Using the endocytic protein epsin1 N-terminal homology domain (ENTH), previously thought to drive fission by hydrophobic insertion, our results show that membrane coverage correlates equally with fission regardless of the hydrophobicity of insertions. Specifically, combining FRET-based measurements of membrane coverage with multiple, independent measurements of membrane vesiculation revealed that fission became spontaneous as steric pressure increased. Further, fission efficiency remained equally potent when helices were replaced by synthetic membrane-binding motifs. These data challenge the view that hydrophobic insertions drive membrane fission, suggesting instead that the role of insertions is to anchor proteins strongly to membrane surfaces, amplifying steric pressure. In line with these conclusions, even green fluorescent protein (GFP) was able to drive fission efficiently when bound to the membrane at high coverage. Our conclusions are further strengthened by the finding that intrinsically disordered proteins, which have large hydrodynamic radii yet lack a defined structure, drove fission with substantially greater potency than smaller, structured proteins.
Journal Article