We study I-V characteristics of periodic square Nb wire networks as a function of temperature in a transverse magnetic eld, with a focus on three llings 2/5, 1/2, and 0.618 that represent very di erent levels of incommensurability. For all three llings, a scaling behavior of I-V characteristics is found, suggesting a nite temperature continuous superconducting phase transition. The lowtemperature I-V characteristics are found to have an exponential form, indicative of the domain-wall excitations.PACS numbers: 74.60.Ge, 64.60.CnThe presence of a quenched symmetry-breaking eld is known to have important consequences on the ordering of low temperature phases in many physical systems. A striking example is the pinning of a two-dimensional (2D) vortex lattice by a periodic potential in a superconducting wire network. Without pinning, a 2D elastic vortex lattice in homogeneous superconducting thin lms would not have long-range translational order at anynite temperature 1] and cannot have long-range superconducting phase coherence even at T = 0. A periodic pinning potential, however, when it is commensurate to the vortex lattice, can induce a gap in the low-energy excitation spectrum 2] and create a new thermodynamic phase 3] of a pinned 2D solid with true long-range translational order, and with superconducting phase coherence 4]. In the presence of a high-order commensurate (or incommensurate) potential, the competition between the vortex-vortex interactions and the vortex-network interactions leads to a whole new class of problems 5{7]. For example, the vortex lattice may: (a) become a 2D \ oating" solid and again lose its translational order and superconducting phase coherence at any temperature 5]; (b) form a metastable \glassy" phase 6]; (c) be pinned in a commensurate phase 7] and thus superconducting at low temperatures. The issue is far from being settled.Closely related to the low-temperature thermodynamic phase, the nature of the superconducting transition of a superconducting network in a magnetic eld is also not well understood. At lling f = 1=2, where f is the fraction of a ux quantum 0 = hc=2e per plaquette, for example, the vortex con guration of the ground state of the system has a checker-board pattern 4]. Thus, the ground state of the system has the discrete symmetry of the two-fold degeneracy as well as the continuous symmetry of an arbitrary global phase change. Two types of excitations are possible: vortex-antivortex pairs of the continuous phase variable and domain walls of the two ground states. If the two types of excitations do not interact, they should lead to two independent transitions 9]: a Kosterlitz-Thouless (KT) transition 8] in the underlying network and an Ising melting transition in the vortex lattice. The superconducting transition will be determined by the one with the lower transition-temperature. Interesting physics arises when the two types of excitations do couple 10]. Due to the screening of the vortex interactions by the domain walls, when the domain wall energy goes to zero ...

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The peak effect (PE) has been observed in a twinned crystal of YBa 2 Cu 3 O 7−δ for H c in the low field range, close to the zero field superconducting transition temperature (T c (0)) . A sharp depinning transition succeeds the peak temperature T p of the PE. The PE phenomenon broadens and its internal structure smoothens out as the field is increased or decreased beyond the interval between 250 Oe and 1000 Oe. Moreover, the PE could not be observed above 10 kOe and below 20 Oe. The locus of the T p (H) values shows a reentrant characteristic with a nose like feature located at T p (H)/T c (0)≈0.99 and H≈100 Oe (where the FLL constant a 0 ≈penetration depth λ). The upper part of the PE curve (0.5 kOe

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In this paper, we analyze the real-time infection data of COVID-19 epidemic for 21 nations up to May 18, 2020. For most of these nations, the total number of infected individuals exhibits a succession of exponential growth and power-law growth before the flattening of the curve. In particular, we find a universal √ t growth before they reach saturation. India, Singapore, and Sri Lanka have reached up to linear growth (I(t) ∼ t), and they are yet to flatten their curves. Russia and Brazil are still in the power-law (t 2 ) growth regime. Thus, the polynomials of the I(t) curves provide valuable information on the stage of the epidemic evolution. Besides these detailed analyses, we compare the predictions of an extended SEIR model and a delay differential equation-based model with the reported infection data and observed good agreement among them, including the √ t behaviour.

Current epidemiological models can in principle model the temporal evolution of a pandemic. However, any such model will rely on parameters that are unknown, which in practice are estimated using stochastic and poorly measured quantities. As a result, an early prediction of the long-term evolution of a pandemic will quickly lose relevance, while a late model will be too late to be useful for disaster management. Unless a model is designed to be adaptive, it is bound either to lose relevance over time, or lose trust and thus not have a second-chance for retraining. We propose a strategy for estimating the number of infections and the number of deaths, that does away with time-series modeling, and instead makes use of a "phase portrait approach." We demonstrate that, with this approach, there is a universality to the evolution of the disease across countries, that can then be used 1 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) : medRxiv preprint to make reliable predictions. These same models can also be used to plan the requirements for critical resources during the pandemic. The approach is designed for simplicity of interpretation, and adaptivity over time. Using our model, we predict the number of infections and deaths in Italy and New York State, based on an adaptive algorithm which uses early available data, and show that our predictions closely match the actual outcomes.We also carry out a similar exercise for India, where in addition to projecting the number of infections and deaths, we also project the expected range of critical resource requirements for hospitalizations in a location.

We study I-V characteristics of periodic square Nb wire networks as a function of temperature in a transverse magnetic eld, with a focus on three llings 2/5, 1/2, and 0.618 that represent very di erent levels of incommensurability. For all three llings, a scaling behavior of I-V characteristics is found, suggesting a nite temperature continuous superconducting phase transition. The lowtemperature I-V characteristics are found to have an exponential form, indicative of the domain-wall excitations.