Criticality and quenched disorder: rare regions vs. Harris criterion

We employ scaling arguments and optimal fluctuation theory to establish a general relation between quantum Griffiths singularities and the Harris criterion for quantum phase transitions in disordered systems. If a clean critical point violates the Harris criterion, it is destabilized by weak disorder. At the same time, the Griffiths dynamical exponent $z'$ diverges upon approaching the transition, suggesting unconventional critical behavior. In contrast, if the Harris criterion is fulfilled, power-law Griffiths singularities can coexist with clean critical behavior but $z'$ saturates at a finite value. We present applications of our theory to a variety of systems including quantum spin chains, classical reaction-diffusion systems and metallic magnets; and we discuss modifications for transitions above the upper critical dimension. Based on these results we propose a unified classification of phase transitions in disordered systems.Comment: 4.5 pages, 1 eps figure, final version as publishe

Facebook intensity, social network support, stability and satisfaction in long-distance and geographically-close romantic relationships:A test of a mediation model

The impetus for this study is the proposition that social network sites (SNSs), like Facebook, can be beneficial for romantic relationships via network support functions. This study investigated a model which proposes that the use of Facebook predicts relationship support from Facebook connections, and this, in turn, predicts relationship stability and satisfaction in romantic relationships. This mediation model was tested on data gathered via an online survey among individuals who use Facebook, who are in long-distance (LDRR, n = 142) and geographically-close romantic relationships (GCRR, n = 314). GCRR participants reported higher levels of Facebook intensity and relationship support, as well as perceived relationship stability and satisfaction than participants in LDRR. Moreover, the results indicated that Facebook intensity predicted higher access to Facebook relationship support in LDRR and GCRR which, in turn, predicted perceived relationship stability and satisfaction in LDRR; and only perceived relationship satisfaction in GCRR. However, Facebook intensity had direct negative impacts on relationship satisfaction in GCRR, and on perceived relationship stability in LDRR. Facebook intensity and Facebook relationship support were not associated with relationship stability in GCRR. This demonstrates the relative importance of SNSs, such as Facebook, in relationship stability for those in LDRR

Help! An Insight into Long Distance Romantic Relationship Advice Sought Online

The purpose of this study was to examine the long-distance romantic relationship (LDRR) advice sought online and see how it relates to previous literature. Reddit posts from the r/LongDistance subreddit were narrowed using an advanced search to find the most popular (upvoted) advice from users. Qualitative, contextual analysis research was used to search for reoccurring themes throughout the advice sought. Results revealed that feelings of uncertainty and anxiety were very common within LDRR, and advice was sought about how to maintain relationships whilst living apart

Rare region effects at classical, quantum, and non-equilibrium phase transitions

Rare regions, i.e., rare large spatial disorder fluctuations, can dramatically change the properties of a phase transition in a quenched disordered system. In generic classical equilibrium systems, they lead to an essential singularity, the so-called Griffiths singularity, of the free energy in the vicinity of the phase transition. Stronger effects can be observed at zero-temperature quantum phase transitions, at nonequilibrium phase transitions, and in systems with correlated disorder. In some cases, rare regions can actually completely destroy the sharp phase transition by smearing. This topical review presents a unifying framework for rare region effects at weakly disordered classical, quantum, and nonequilibrium phase transitions based on the effective dimensionality of the rare regions. Explicit examples include disordered classical Ising and Heisenberg models, insulating and metallic random quantum magnets, and the disordered contact process.Comment: Topical review, 68 pages, 14 figures, final version as publishe

Broadening of a nonequilibrium phase transition by extended structural defects

We study the effects of quenched extended impurities on nonequilibrium phase transitions in the directed percolation universality class. We show that these impurities have a dramatic effect: they completely destroy the sharp phase transition by smearing. This is caused by rare strongly coupled spatial regions which can undergo the phase transition independently from the bulk system. We use extremal statistics to determine the stationary state as well as the dynamics in the tail of the smeared transition, and we illustrate the results by computer simulations.Comment: 4 pages, 4 eps figures, final version as publishe

MetaMask: Revisiting Dimensional Confounder for Self-Supervised Learning

As a successful approach to self-supervised learning, contrastive learning aims to learn invariant information shared among distortions of the input sample. While contrastive learning has yielded continuous advancements in sampling strategy and architecture design, it still remains two persistent defects: the interference of task-irrelevant information and sample inefficiency, which are related to the recurring existence of trivial constant solutions. From the perspective of dimensional analysis, we find out that the dimensional redundancy and dimensional confounder are the intrinsic issues behind the phenomena, and provide experimental evidence to support our viewpoint. We further propose a simple yet effective approach MetaMask, short for the dimensional Mask learned by Meta-learning, to learn representations against dimensional redundancy and confounder. MetaMask adopts the redundancy-reduction technique to tackle the dimensional redundancy issue and innovatively introduces a dimensional mask to reduce the gradient effects of specific dimensions containing the confounder, which is trained by employing a meta-learning paradigm with the objective of improving the performance of masked representations on a typical self-supervised task. We provide solid theoretical analyses to prove MetaMask can obtain tighter risk bounds for downstream classification compared to typical contrastive methods. Empirically, our method achieves state-of-the-art performance on various benchmarks.Comment: Accepted by NeurIPS 202

Dual Axis Solar Tracking System for Solar Panel

Sustainable energy systems are necessary for the economic growth and a healthy environment. India is currently suffering from an economic slump and acute fuel shortage. To overcome these issues the use of renewable energy resources needs to be enhanced manifold. The main purpose of this paper is to present a tracking system which will cause better alignment of solar panel with sunlight and to harvest solar power. The proposed system changes its direction in two axis to trace the coordinate of sunlight by detecting change in light intensity through light dependent resistors. Hardware testing of the proposed system is done for checking the system ability to track and follow the sunlight in an efficient way. Dual axis solar tracking system superiority over stationary solar panel is also presented

Phases and phase transitions in disordered quantum systems

These lecture notes give a pedagogical introduction to phase transitions in disordered quantum systems and to the exotic Griffiths phases induced in their vicinity. We first review some fundamental concepts in the physics of phase transitions. We then derive criteria governing under what conditions spatial disorder or randomness can change the properties of a phase transition. After introducing the strong-disorder renormalization group method, we discuss in detail some of the exotic phenomena arising at phase transitions in disordered quantum systems. These include infinite-randomness criticality, rare regions and quantum Griffiths singularities, as well as the smearing of phase transitions. We also present a number of experimental examples.Comment: Pedagogical introduction to strong disorder physics at quantum phase transitions. Based on lectures given at the XVII Training Course in the Physics of Strongly Correlated Systems in Vietri sul Mare, Italy in October 2012. Submitted to the proceedings of this school. 60 pages and 23 figures. Builds on material reviewed in arXiv:cond-mat/0602312 and arXiv:1005.270

Dust in a few southern H II regions

The property of dust in four southern H II region/molecular cloud complexes (RCW 108, RCW 57, RCW 122, and G351.6-1.3) was discussed. These regions were observed at an effective wavelength of 150 micron using TIFR balloon borne 1 m telescope and deconvolved maps with a resolution of 1 min were obtained. The data were combined with other available data to derive the properties of the infrared emitting dust in these regions

Rare regions and Griffiths singularities at a clean critical point: The five-dimensional disordered contact process

We investigate the nonequilibrium phase transition of the disordered contact process in five space dimensions by means of optimal fluctuation theory and Monte Carlo simulations. We find that the critical behavior is of mean-field type, i.e., identical to that of the clean five-dimensional contact process. It is accompanied by off-critical power-law Griffiths singularities whose dynamical exponent $z'$ saturates at a finite value as the transition is approached. These findings resolve the apparent contradiction between the Harris criterion which implies that weak disorder is renormalization-group irrelevant and the rare-region classification which predicts unconventional behavior. We confirm and illustrate our theory by large-scale Monte-Carlo simulations of systems with up to $70^5$ sites. We also relate our results to a recently established general relation between the Harris criterion and Griffiths singularities [Phys. Rev. Lett. {\bf 112}, 075702 (2014)], and we discuss implications for other phase transitions.Comment: 10 pages, 5 eps figures included, applies the optimal fluctuation theory of arXiv:1309.0753 to the contact proces