搜索结果：1990s

Blazars are a subclass of radio-loud active galactic nuclei (AGNs) that display strong multi-wavelength variability on diverse timescales ranging from years down to minutes. In the last 1.5 decades, there have been occasional detections of quasi-periodic oscillations in several blazars in their time series data. We search for quasi-periodic oscillations (QPOs) in the 37 GHz radio band light curve of the flat-spectrum radio quasar Ton~599 made at the RT-22 radio telescope in Simeiz, Crimea, from 1990 to 2020. To identify and quantify the QPO nature of this radio light curve of Ton 599, we used the Lomb-Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses. We report the detection of a likely QPO of about 2.4 years in the 37 GHz radio light curves of Ton 599. We briefly discuss possible emission models for radio-loud active galactic nuclei that could explain such QPOs with periods of a few years.

The families of graphs defined by a certain type of system of equations over commutative rings have been studied and used since 1990s. This survey presents these families and their applications related to graphs, digraphs, and hypergraphs. Some open problems and conjectures are mentioned.

Background:Chronic kidney disease is one of the most prevalent non-communicable health issues globally, and high body mass index plays a significant role in the onset and progression of chronic kidney disease. Methods: Data on the disease burden attributable to high body mass index were retrieved from the 2021 Global Burden of Disease, Injuries, and Risk Factors Study . The global cases, age-standardized mortality rate , and age-standardized disability-adjusted life years attributable to high body mass index were estimated based on age, sex, geographic location, and the Social-demographic Index (SDI). The estimated annual percentage change was calculated to quantify trends in ASMR and ASDR from 1990 to 2019. Decomposition and frontier analyses were conducted to understand the drivers behind changes in burden and to identify top-performing countries. Inequality analysis was performed to assess disparities in burden across different SDI levels. The Bayesian age-period-cohort model was used to predict the disease burden up to 2035.Results: In 2021, there were 4,643.41 global deaths and 2,514,227.16 DALYs attributable to high body mass index-related CKD, more than triple the figures fr

A configuration of the NCAR WRF-Hydro model was sought using well established data models to guide the initial hydrologic model setup, as well as a seasonal streamflow post-processing by neural networks. Discharge was simulated using an eastern Canadian river network at two-km resolution. The river network was taken from a digital elevation model that was made to conform to observed catchment boundaries. Perturbations of a subset of model parameters were examined with reference to streamflow from 25 gauged catchments during the 2019 warm season. A data model defines the similarity of modelled streamflow to observations, and improvements were found in about half the individual catchments. With reference to 183 gauged catchments (1990-2022), further improvements were obtained at monthly and annual scales by neural network post-processing that targets all catchments at once as well as individual catchments. This seasonal calibration was applied to uncoupled WRF-Hydro simulations for the 1990-2100 warming period. Historic and future forcing were provided, respectively, by a European Centre for Medium-Range Weather Forecasting reanalysis (ERA5), and by a WRF atmospheric model downscalin

We revisit the classical analysis of Karp, Vazirani, and Vazirani (KVV, STOC~1990), which established the well-known upper bound of $1 - 1/e$ as the limiting proportion of vertices that can be matched by any online procedure in a canonical bipartite structure. Although foundational, the original analysis contains several inaccuracies, including a fundamental technical gap in the treatment of the underlying discrete process. We give a transparent and fully rigorous reconstruction of the KVV argument by reformulating the evolution of available neighbors as a discrete-time death process and deriving a sharp upper bound via a simple factor-revealing linear program that captures the correct recurrence structure. This yields a precise bound $\lceil n(1 - 1/e) + 2 - 1/e \rceil$ on the expected number of matched vertices, refining the classical claim $n(1 - 1/e) + o(n)$. Our goal is not to optimize this upper bound, but to provide a mathematically sound and conceptually clean correction of the classical KVV analysis, while remaining faithful to its original combinatorial framework.

This study presents a unified, distribution-aware, and complexity-informed framework for understanding equity return dynamics in the Indian market, using 34 years (1990 to 2024) of Nifty 50 index data. Addressing a key gap in the literature, we demonstrate that the price to earnings ratio, as a valuation metric, may probabilistically map return distributions across investment horizons spanning from days to decades. Return profiles exhibit strong asymmetry. One-year returns show a 74 percent probability of gain, with a modal return of 10.67 percent and a reward-to-risk ratio exceeding 5. Over long horizons, modal CAGRs surpass 13 percent, while worst-case returns remain negative for up to ten years, defining a historical trapping period. This horizon shortens to six years in the post-1999 period, reflecting growing market resilience. Conditional analysis of the P/E ratio reveals regime-dependent outcomes. Low valuations (P/E less than 13) historically show zero probability of loss across all horizons, while high valuations (P/E greater than 27) correspond to unstable returns and extended breakeven periods. To uncover deeper structure, we apply tools from complexity science. Entropy,

We present a comprehensive study on the emergence of Computational Social Science (CSS) - an interdisciplinary field leveraging computational methods to address social science questions - and its impact on adjacent social sciences. We trained a robust CSS classifier using papers from CSS-focused venues and applied it to 11 million papers spanning 1990 to 2021. Our analysis yielded three key findings. First, there were two critical inflections in the rise of CSS. The first occurred around 2005 when psychology, politics, and sociology began engaging with CSS. The second emerged in approximately 2014 when economics finally joined the trend. Sociology is currently the most engaged with CSS. Second, using the density of yearly knowledge embeddings constructed by advanced transformer models, we observed that CSS initially lacked a cohesive identity. From the early 2000s to 2014, however, it began to form a distinct cluster, creating boundaries between CSS and other social sciences, particularly in politics and sociology. After 2014, these boundaries faded, and CSS increasingly blended with the social sciences. Third, shared data-driven methods homogenized CSS papers across disciplines, w

The study aims to highlight the growth and development of Indo-German collaborative research over the past three decades. Moreover, this study encompasses an in-depth examination of funding acknowledgements to gain valuable insights into the financial support that underpins these collaborative endeavors. Together with this paper, we provide an openly accessible dataset of Indo-German research articles for further and reproducible research activities (the "Indo-German Literature Dataset"). The data were retrieved from the Web of Science (WoS) database from the year 1990 till the 30th of November 2022. A total of 36,999 records were retrieved against the employed query. Acknowledged entities were extracted using a NER model specifically trained for this task. Interrelations between the extracted entities and scientific domains, lengths of acknowledgement texts, number of authors and affiliations, number of citations, and gender of the first author, as well as collaboration patterns between Indian and German funders were examined. The study brings to light that Physics, Chemistry, Materials Science, Astronomy and Astrophysics, and Engineering prominently dominate the Indo-German colla

In Central Europe, the occurrence of different weather regimes (WRs) plays a major role in spatiotemporal temperature and precipitation patterns. In the context of increasingly extreme summers, this study focuses on European summer WRs (June-August, JJA) over the last three decades (1990-2019), and aims to examine the changing characteristics of these WRs and their potential implications. In addition, based on ERA5 reanalysis data, the WR representation from a carefully preselected, small ensemble of global general circulation models (GCMs) is analyzed. A methodological refinement concerns the combination of Self-Organizing Maps (SOM) with a novel GCM selection technique, which enhances the robustness of the simulated large-scale circulation patterns. WRs are defined using daily sea level pressure (SLP) and wind in the upper troposphere. Results reveal that the SOM captures predominant European summer synoptic patterns, and the salient result is a positive trend in 2 m air temperature across nearly all WRs. The selected GCMs - MPI-ESM1-2-LR r29i1p1f1, CanESM5 r1i1p1f1 and MRI-ESM2-0 r5i1p1f1 - identify WRs correctly and ERA5-based results are always within the range of this small G

Cherenkov techniques are widely used in astroparticle experiments. This article reviews the various detection principles and the corresponding experiments, including some of the physics breakthroughs. In particular, it traces the development since the mid of the 1990s, a period when the field took a particularly dynamic development.

Since the inception of the first web page three decades back, the Web has evolved considerably, from static HTML pages in the beginning to the dynamic web pages of today, from mainly the text-based pages of the 1990s to today's multimedia rich pages, etc. Although much of this is known anecdotally, to our knowledge, there is no quantitative documentation of the extent and timing of these changes. This paper attempts to address this gap in the literature by looking at the top 100 Alexa websites for over 25 years from the Internet Archive or the "Wayback Machine", archive.org. We study the changes in popularity, from Geocities and Yahoo! in the mid-to-late 1990s to the likes of Google, Facebook, and Tiktok of today. We also look at different categories of websites and their popularity over the years and find evidence for the decline in popularity of news and education-related websites, which have been replaced by streaming media and social networking sites. We explore the emergence and relative prevalence of different MIME-types (text vs. image vs. video vs. javascript and json) and study whether the use of text on the Internet is declining.

We discover that the distribution of (frequency and phase) resonances plays a role in determining the spectral type of supercritical quasi-periodic Schrödinger operators. In particular, we disprove the second spectral transition line conjecture of Jitomirskaya in the early 1990s.

Context. The relation between solar surface rotation and sunspot activity still remains open. Sunspot activity has dramatically reduced in solar cycle 24 and several solar activity indices and flux measurements experienced unprecedentedly low levels during the last solar minimum. Aims. We aim to reveal the momentary variation of solar surface rotation, especially during the recent years of reducing solar activity. Methods. We used a dynamic, differentially rotating reference system to determine the best-fit annual values of the differential rotation parameters of active longitudes of solar X-ray flares and sunspots in 1977-2012. Results. The evolution of rotation of solar active longitudes obtained with X-ray flares and with sunspots is very similar. Both hemispheres speed up since the late 1990s, with the southern hemisphere rotating slightly faster than the north. Earlier, in 1980s, rotation in the northern hemisphere was considerably faster, but experienced a major decrease in the early 1990s. On the other hand, little change was found in the southern rotation during these decades. This led to a positive asymmetry in north-south rotation rate in the early part of the time interv

Demographic indicators are an essential element in considering various problems in the social economy, such as predicting economic fluctuations and establishing policies. The literature widely discusses the growth of the world population or issues pertaining to its aging, but has given little to no attention to population structures and transition patterns. In this article, we take advantage of the characteristics of compositional data to examine the transition of the world population structure. Using the Aitchison distance, we examine the similarity of the world population structure from the 1990s to 2080 and that of countries and regions in 2015 and create maps to illustrate the results. Accordingly, we identify the following countries and regions as epitomes of the world population structure through different periods: India, Northern Africa and South Africa, in the 1990s, South America in 2015 to 2030, Oceania and Northern America in 2040, Uruguay and Puerto Rico in 2050 to 2060, and Italy and Japan in the distant future. We then cluster countries based on the similarity of their population structures in 2015 and correspond each cluster to a certain period. We found that Russia

The generation of political event data has remained much the same since the mid-1990s, both in terms of data acquisition and the process of coding text into data. Since the 1990s, however, there have been significant improvements in open-source natural language processing software and in the availability of digitized news content. This paper presents a new, next-generation event dataset, named Phoenix, that builds from these and other advances. This dataset includes improvements in the underlying news collection process and event coding software, along with the creation of a general processing pipeline necessary to produce daily-updated data. This paper provides a face validity checks by briefly examining the data for the conflict in Syria, and a comparison between Phoenix and the Integrated Crisis Early Warning System data.