3,437 research outputs found
Indefinite quadratic forms and the invariance of the interval in Special Relativity
A simple theorem on proportionality of indefinite real quadratic forms is
proved, and is used to clarify the proof of the invariance of the interval in
Special Relativity from Einstein's postulate on the universality of the speed
of light; students are often rightfully confused by the incomplete or incorrect
proofs given in many texts. The result is illuminated and generalized using
Hilbert's Nullstellensatz, allowing one form to be a homogeneous polynomial
which is not necessarily quadratic. Also a condition for simultaneous
diagonalizabilityof semi-definite real quadratic functions is given.Comment: 6 pages, no figure
Iterated function systems with a given continuous stationary distribution
For any continuous probability measure on we construct an
IFS with probabilities having as its unique measure-attractor.Comment: 7 pages, 3 figure
Building Bulletin 77 – Ergonomic content review
Building Bulletin 77 – Ergonomic content revie
See and Read: Detecting Depression Symptoms in Higher Education Students Using Multimodal Social Media Data
Mental disorders such as depression and anxiety have been increasing at
alarming rates in the worldwide population. Notably, the major depressive
disorder has become a common problem among higher education students,
aggravated, and maybe even occasioned, by the academic pressures they must
face. While the reasons for this alarming situation remain unclear (although
widely investigated), the student already facing this problem must receive
treatment. To that, it is first necessary to screen the symptoms. The
traditional way for that is relying on clinical consultations or answering
questionnaires. However, nowadays, the data shared at social media is a
ubiquitous source that can be used to detect the depression symptoms even when
the student is not able to afford or search for professional care. Previous
works have already relied on social media data to detect depression on the
general population, usually focusing on either posted images or texts or
relying on metadata. In this work, we focus on detecting the severity of the
depression symptoms in higher education students, by comparing deep learning to
feature engineering models induced from both the pictures and their captions
posted on Instagram. The experimental results show that students presenting a
BDI score higher or equal than 20 can be detected with 0.92 of recall and 0.69
of precision in the best case, reached by a fusion model. Our findings show the
potential of large-scale depression screening, which could shed light upon
students at-risk.Comment: This article was accepted (15 November 2019) and will appear in the
proceedings of ICWSM 202
Portfolio Optimization and the Random Magnet Problem
Diversification of an investment into independently fluctuating assets
reduces its risk. In reality, movement of assets are are mutually correlated
and therefore knowledge of cross--correlations among asset price movements are
of great importance. Our results support the possibility that the problem of
finding an investment in stocks which exposes invested funds to a minimum level
of risk is analogous to the problem of finding the magnetization of a random
magnet. The interactions for this ``random magnet problem'' are given by the
cross-correlation matrix {\bf \sf C} of stock returns. We find that random
matrix theory allows us to make an estimate for {\bf \sf C} which outperforms
the standard estimate in terms of constructing an investment which carries a
minimum level of risk.Comment: 12 pages, 4 figures, revte
Traveler Gun Irrigation of Field Grown Nursery Stock
The objective of this study was to determine annual irrigation costs for field-grown plants in Ohio by species of plant and size of firm. This objective was accomplished by synthesizing two model field nurseries using an economic engineering approach. Once the nurseries were simulated, growing space was divided into five equal parts with each segment being assigned a plant group. In the 50-acre nursery each group was allocated 8 acres of field production plus corresponding space in the propagation house, overwintering facility, holding area, and field bed area. In the 200-acre nursery each plant group was allocated 35 acres, plus corresponding space in the central facility. In each plant group, one specific species was chosen as representative for the group. Total costs of installing irrigation systems were estimated at about 167,800 for a 200-acre field nursery. Total annual costs for irrigating the 50-acre nursery were 0.73 for slow growing evergreens (Taxus), 0.49 for deciduous shrubs (Viburnum), 1.11 for ornamental trees (Malus), and averaged 35,355. Per salable plant costs were 0.28 for fast growing evergreens (Juniperus), 0.86 for shade trees (Acer rubrum), 0.39 for all species. Costs of irrigation were about 2.9% of total annual costs for the 200-acre nursery. Costs of irrigation averaged approximately 87% higher per salable plant in the 50-acre nursery than in the 200-acre. Large-size commercial field nurseries use equipment and labor more efficiently than small-sized nurseries. As a result, large nurseries have a lower cost of irrigation per salable plant
Multiscaled Cross-Correlation Dynamics in Financial Time-Series
The cross correlation matrix between equities comprises multiple interactions
between traders with varying strategies and time horizons. In this paper, we
use the Maximum Overlap Discrete Wavelet Transform to calculate correlation
matrices over different timescales and then explore the eigenvalue spectrum
over sliding time windows. The dynamics of the eigenvalue spectrum at different
times and scales provides insight into the interactions between the numerous
constituents involved.
Eigenvalue dynamics are examined for both medium and high-frequency equity
returns, with the associated correlation structure shown to be dependent on
both time and scale. Additionally, the Epps effect is established using this
multivariate method and analyzed at longer scales than previously studied. A
partition of the eigenvalue time-series demonstrates, at very short scales, the
emergence of negative returns when the largest eigenvalue is greatest. Finally,
a portfolio optimization shows the importance of timescale information in the
context of risk management
Mortality risk and mental disorders: longitudinal results from the Upper Bavarian Study
The object of the study was the assessment of the mortality risk for persons with a mental disorder in an unselected representative community sample assessed longitudinally. Subjects from a rural area in Upper Bavaria (Germany) participated in semi-structured interviews conducted by research physicians in the 1970s (first assessment) and death-certificate diagnoses were obtained after an interval up to 13 years later. The sample consisted of 1668 community residents aged 15 years and over. Cox regression estimates resulted in an odds ratio of 1·35 (confidence interval 1·01 to 1·81) for persons with a mental disorder classified as marked to very severe. The odds ratio increased with increasing severity of mental illness from 1·04 for mild disorders, 1·30 for marked disorders, to 1·64 for severe or very severe disorders. The relative risk (odds ratio) for persons with a mental disorder only and no somatic disorder was 1·22, for persons with only a somatic disorder 2·00, and for those with both a mental and a somatic disorder 2·13. The presence of somatic illness was responsible for most of the excess mortality. Somatic disorders associated with excess mortality in mental disorders were diseases of the nervous system or sensory organs, diseases of the circulatory system, diseases of the gastrointestinal tract, and diseases of the skeleton, muscles and connective tissue (ICD-8). Thus, while mental illness alone had a limited effect on excess mortality, comorbidity with certain somatic disorders had a significant effec
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