Interaction induced dimerization in zigzag single wall carbon nanotubes

We derive a low-energy effective model of metallic zigzag carbon nanotubes at half filling. We show that there are three important features characterizing the low-energy properties of these systems: the long-range Coulomb interaction, umklapp scattering and an explicit dimerization generated by interactions. The ratio of the dimerization induced gap and the Mott gap induced by the umklapp interactions is dependent on the radius of the nanotube and can drive the system through a quantum phase transition with SU(2)_1 quantum symmetry. We consider the physical properties of the phases on either side of this transition which should be relevant for realistic nanotubes.Comment: 8 pages, 5 figure

{\mu}Split: efficient image decomposition for microscopy data

We present {\mu}Split, a dedicated approach for trained image decomposition in the context of fluorescence microscopy images. We find that best results using regular deep architectures are achieved when large image patches are used during training, making memory consumption the limiting factor to further improving performance. We therefore introduce lateral contextualization (LC), a memory efficient way to train powerful networks and show that LC leads to consistent and significant improvements on the task at hand. We integrate LC with U-Nets, Hierarchical AEs, and Hierarchical VAEs, for which we formulate a modified ELBO loss. Additionally, LC enables training deeper hierarchical models than otherwise possible and, interestingly, helps to reduce tiling artefacts that are inherently impossible to avoid when using tiled VAE predictions. We apply {\mu}Split to five decomposition tasks, one on a synthetic dataset, four others derived from real microscopy data. LC achieves SOTA results (average improvements to the best baseline of 2.36 dB PSNR), while simultaneously requiring considerably less GPU memory.Comment: Published at ICCV 2023. 10 pages, 7 figures, 9 pages supplement, 8 supplementary figure

The Gravity Dual of the Ising Model

We evaluate the partition function of three dimensional theories of gravity in the quantum regime, where the AdS radius is Planck scale and the central charge is of order one. The contribution from the AdS vacuum sector can - with certain assumptions - be computed and equals the vacuum character of a minimal model CFT. The torus partition function is given by a sum over geometries which is finite and computable. For generic values of Newton's constant G and the AdS radius L the result has no Hilbert space interpretation, but in certain cases it agrees with the partition function of a known CFT. For example, the partition function of pure Einstein gravity with G=3L equals that of the Ising model, providing evidence that these theories are dual. We also present somewhat weaker evidence that the 3-state and tricritical Potts models are dual to pure higher spin theories of gravity based on SL(3) and E_6, respectively.Comment: 42 page

Laser irradiated foam targets: absorption and radiative properties

An experimental campaign to characterize the laser radiation absorption of foam targets and the subsequent emission of radiation from the produced plasma was carried out in the ABC facility of the ENEA Research Center in Frascati (Rome). Different targets have been used: plastic in solid or foam state and aluminium targets. The activated different diagnostics allowed to evaluate the plasma temperature, the density distribution, the fast particle spectrum and the yield of the X-Ray radiation emitted by the plasma for the different targets. These results confirm the foam homogenization action on laser-plasma interaction, mainly attributable to the volume absorption of the laser radiation propagating in such structured materials. These results were compared with simulation absorption models of the laser propagating into a foam target

Current fluctuations in stochastically resetting particle systems

We consider a system of non-interacting particles on a line with initial positions distributed uniformly with density $\rho$ on the negative half-line. We consider two different models: (i) each particle performs independent Brownian motion with stochastic resetting to its initial position with rate $r$ and (ii) each particle performs run and tumble motion, and with rate $r$ its position gets reset to its initial value and simultaneously its velocity gets randomised. We study the effects of resetting on the distribution $P(Q,t)$ of the integrated particle current $Q$ up to time $t$ through the origin (from left to right). We study both the annealed and the quenched current distributions and in both cases, we find that resetting induces a stationary limiting distribution of the current at long times. However, we show that the approach to the stationary state of the current distribution in the annealed and the quenched cases are drastically different for both models. In the annealed case, the whole distribution $P_{\rm an}(Q,t)$ approaches its stationary limit uniformly for all $Q$. In contrast, the quenched distribution $P_{\rm qu}(Q,t)$ attains its stationary form for $Q<Q_{\rm crit}(t)$, while it remains time-dependent for $Q > Q_{\rm crit}(t)$. We show that $Q_{\rm crit}(t)$ increases linearly with $t$ for large $t$. On the scale where $Q \sim Q_{\rm crit}(t)$, we show that $P_{\rm qu}(Q,t)$ has an unusual large deviation form with a rate function that has a third-order phase transition at the critical point. We have computed the associated rate functions analytically for both models. Using an importance sampling method that allows to probe probabilities as tiny as $10^{-14000}$, we were able to compute numerically this non-analytic rate function for the resetting Brownian dynamics and found excellent agreement with our analytical prediction.Comment: 26 pages, 6 figure

The two-boundary Temperley-Lieb algebra

We study a two-boundary extension of the Temperley-Lieb algebra which has recently arisen in statistical mechanics. This algebra lies in a quotient of the affine Hecke algebra of type C and has a natural diagrammatic representation. The algebra has three parameters and, for generic values of these, we determine its representation theory. We use the action of the centre of the affine Hecke algebra to show that all irreducible representations lie within a finite dimensional diagrammatic quotient. These representations are fully characterised by an additional parameter related to the action of the centre. For generic values of this parameter there is a unique representation of dimension 2^N and we show that it is isomorphic to a tensor space representation. We construct a basis in which the Gram matrix is diagonal and use this to discuss the irreducibility of this representation.Comment: 45 pages Latex, 21 eps figures, revised versio

Asymptotics of the instantons of Painleve I

The 0-instanton solution of Painlev\'e I is a sequence $(u_{n,0})$ of complex numbers which appears universally in many enumerative problems in algebraic geometry, graph theory, matrix models and 2-dimensional quantum gravity. The asymptotics of the 0-instanton $(u_{n,0})$ for large $n$ were obtained by the third author using the Riemann-Hilbert approach. For $k=0,1,2,...$, the $k$-instanton solution of Painlev\'e I is a doubly-indexed sequence $(u_{n,k})$ of complex numbers that satisfies an explicit quadratic non-linear recursion relation. The goal of the paper is three-fold: (a) to compute the asymptotics of the 1-instanton sequence $(u_{n,1})$ to all orders in $1/n$ by using the Riemann-Hilbert method, (b) to present formulas for the asymptotics of $(u_{n,k})$ for fixed $k$ and to all orders in $1/n$ using resurgent analysis, and (c) to confirm numerically the predictions of resurgent analysis. We point out that the instanton solutions display a new type of Stokes behavior, induced from the tritronqu\'ee Painlev\'e transcendents, and which we call the induced Stokes phenomenon. The asymptotics of the 2-instanton and beyond exhibits new phenomena not seen in 0 and 1-instantons, and their enumerative context is at present unknown.Comment: 29 pages, 8 figure

Shape-specific microfabricated particles for biomedical applications: a review

The storied history of controlled the release systems has evolved over time; from degradable drug-loaded sutures to monolithic zero-ordered release devices and nano-sized drug delivery formulations. Scientists have tuned the physico-chemical properties of these drug carriers to optimize their performance in biomedical/pharmaceutical applications. In particular, particle drug delivery systems at the micron size regime have been used since the 1980s. Recent advances in micro and nanofabrication techniques have enabled precise control of particle size and geometry–here we review the utility of microplates and discoidal polymeric particles for a range of pharmaceutical applications. Microplates are defined as micrometer scale polymeric local depot devices in cuboid form, while discoidal polymeric nanoconstructs are disk-shaped polymeric particles having a cross-sectional diameter in the micrometer range and a thickness in the hundreds of nanometer range. These versatile particles can be used to treat several pathologies such as cancer, inflammatory diseases and vascular diseases, by leveraging their size, shape, physical properties (e.g., stiffness), and component materials, to tune their functionality. This review highlights design and fabrication strategies for these particles, discusses their applications, and elaborates on emerging trends for their use in formulations. GRAPHICAL ABSTRACT: [Image: see text

Engraftment of human amniotic fluid stem cells (AFSCs) in calvarial bone of immunodeficient mice

AFSCs represent an attractive cell model for transplantation therapy due to the lack of significant immunogenicity, tumorigenicity and ethical issues (De Coppi et al., 2007). Although AFSCs have been investigated for bone repair, the cellular distribution and post-implantation viability remain key issues (Dupont et al., 2010). The present study was aimed at investigating whether AFSCs could improve bone healing in a calvarial defect model using immunodeficient mice. For this purpose AFSCs were transfected with a lentiviral vector expressing a ubiquitously directed red fluorescent protein-cherry. For in vivo experiments a critical size (3.5 mm) calvarial defect was developed in NOD scid gamma (NSG) immunodeficient mice. Human AFSCs were expanded in vitro and transfected at the 1st passage, then transplanted in vivo at the lesion sites after being loaded on HEALOS® scaffold (cross-linked collagen fibers fully coated with hydroxyapatite) appropriately shaped to cover the bone lesion. The calvarial defect was filled with the scaffold alone in control mice. Six weeks after implantation all animals were subjected to a skull X-ray before being sacrificed. Calvarial bone specimens were fixed in paraphormaldehyde, cryopreserved with sucrose and embedded in Cryomatrix TM resin. Sections were observed under fluorescence microscopy to detect the cherry-red signal, and then stained with haematoxylin-eosin solution to better analyze histological structures. Radiography scans of ex vivo bone explants demonstrated the presence of qualitatively and quantitatively mineralized tissue levels in the defect. Light microscopy observations revealed a major fibrous reaction in mice specimens treated with the scaffold supplemented with AFSCs compared with mice treated with the cell-free scaffold. The presence of cherry-positive AFSCs was recognized in the newly formed fibrous bone often around the scaffold and close to newly formed vessels. Our findings indicate that undifferentiated AFSCs seeded on a collagen scaffold can engraft in a host bone contributing to new bone and vessel formation. These preliminary observations pave the way to the use of new bioengineered constructs of stem cell–collagen scaffold for correcting large cranial defects in animal models and human subjects