261 research outputs found
Local effects of redundant terrestrial and GPS-based tie vectors in ITRF-like combinations
No full textTie vectors (TVs) between co-located space geodetic
instruments are essential for combining terrestrial reference
frames (TRFs) realised using different techniques. They
provide relative positioning between instrumental reference
points (RPs) which are part of a global geodetic network
such as the international terrestrial reference frame (ITRF).
This paper gathers the set of very long baseline interferometry
(VLBI)–global positioning system (GPS) local ties
performed at the observatory of Medicina (Northern Italy)
during the years 2001–2006 and discusses some important
aspects related to the usage of co-location ties in the combinations
of TRFs. Two measurement approaches of local
survey are considered here: a GPS-based approach and a
classical approach based on terrestrial observations (i.e.
angles, distances and height differences). The behaviour of terrestrial local ties, which routinely join combinations of
space geodetic solutions, is compared to that of GPS-based
local ties. In particular, we have performed and analysed different
combinations of satellite laser ranging (SLR), VLBI
and GPS long term solutions in order to (i) evaluate the
local effects of the insertion of the series of TVs computed
at Medicina, (ii) investigate the consistency of GPS-based
TVs with respect to space geodetic solutions, (iii) discuss
the effects of an imprecise alignment of TVs from a local to
a global reference frame. Results of ITRF-like combinations
show that terrestrial TVs originate the smallest residuals in
all the three components. In most cases, GPS-based TVs fit
space geodetic solutions very well, especially in the horizontal
components (N, E). On the contrary, the estimation of
the VLBI RP Up component through GPS technique appears
to be awkward, since the corresponding post fit residuals
are considerably larger. Besides, combination tests including
multi-temporal TVs display local effects of residual redistribution,
when compared to those solutions where Medicina
TVs are added one at a time. Finally, the combination of
TRFs turns out to be sensitive to the orientation of the local
tie into the global frame
AUTHOR VERIFICATION OF ELECTRONIC MESSAGING SYSTEMS
No full textMessaging systems have become a hugely popular new paradigm for sending and delivering text messages; however, online messaging platforms have also become an ideal place for criminals due to their anonymity, ease of use and low cost. Therefore, the ability to verify the identity of individuals involved in criminal activity is becoming increasingly important. The majority of research in this area has focused on traditional authorship problems that deal with single-domain datasets and large bodies of text. Few research studies have sought to explore multi-platform author verification as a possible solution to problems around forensics and security. Therefore, this research has investigated the ability to identify individuals on messaging systems, and has applied this to the modern messaging platforms of Email, Twitter, Facebook and Text messages, using different single-domain datasets for population-based and user-based verification approaches. Through a novel technique of cross-domain research using real scenarios, the domain incompatibilities of profiles from different distributions has been assessed, based on real-life corpora using data from 50 authors who use each of the aforementioned domains. The results show that the use of linguistics is likely be similar between platforms, on average, for a population-based approach. The best corpus experimental result achieved a low EER of 7.97% for Text messages, showing the usefulness of single-domain platforms where the use of linguistics is likely be similar, such as Text messages and Emails. For the user-based approach, there is very little evidence of a strong correlation of stylometry between platforms. It has been shown that linguistic features on some individual platforms have features in common with other platforms, and lexical features play a crucial role in the similarities between users’ modern platforms. Therefore, this research shows that the ability to identify individuals on messaging platforms may provide a viable solution to problems around forensics and security, and help against a range of criminal activities, such as sending spam texts, grooming children, and encouraging violence and terrorism
A comment on the article “A collinearity diagnosis of the GNSS geocenter determination” by P. Rebischung, Z. Altamimi, and T. Springer
No full textMeindl et al. (Adv Space Res 51(7):1047–1064, 2013) showed that the geocenter z -component estimated from observations of global navigation satellite systems (GNSS) is strongly correlated to a particular parameter of the solar radiation pressure (SRP) model developed by Beutler et al. (Manuscr Geod 19:367–386, 1994). They analyzed the forces caused by SRP and the impact on the satellites’ orbits. The authors achieved their results using perturbation theory and celestial mechanics. Rebischung et al. (J Geod doi:10.1016/j.asr.2012.10.026, 2013) also deal with the geocenter determination with GNSS. The authors carried out a collinearity diagnosis of the associated parameter estimation problem. They conclude “without much exaggerating that current GNSS are insensitive to any component of geocenter motion”. They explain this inability by the high degree of collinearity of the geocenter coordinates mainly with satellite clock corrections. Based on these results and additional experiments, they state that the conclusions drawn by Meindl et al. (Adv Space Res 51(7):1047–1064, 2013) are questionable. We do not agree with these conclusions and present our arguments in this article. In the first part, we review and highlight the main characteristics of the studies performed by Meindl et al. (Adv Space Res 51(7):1047–1064, 2013) to show that the experiments are quite different from those performed by Rebischung et al. (J Geod doi:10.1016/j.asr.2012.10.026,2013) . In the second part, we show that normal equation (NEQ) systems are regular when estimating geocenter coordinates, implying that the covariance matrices associated with the NEQ systems may be used to assess the sensitivity to geocenter coordinates in a standard way. The sensitivity of GNSS to the components of the geocenter is discussed. Finally, we comment on the arguments raised by Rebischung et al. (J Geod doi:10.1016/j.asr.2012.10.026, 2013) against the results of Meindl et al. (Adv Space Res 51(7):1047–1064, 2013)
Awareness of the Consumption of Dietary Supplements among Students in a University in Saudi Arabia
No full textThe dietary supplement market in Saudi Arabia is growing alongside the number of Saudis consuming dietary supplements. It is therefore increasingly important for healthcare personnel to understand the consumption rate of dietary supplements, whether they are used wisely, and the know-how concerning their use and dosage. The purpose of this study was to clarify the overall awareness of dietary supplement consumption among female students of Princess Nourah Bint Abdulrahman University, Riyadh, Saudi Arabia. Using a descriptive approach, data were collected from 759 female students (mean age = 22.1 ± 1.7 years) via an electronic survey. All participants reported having consumed dietary supplements at some point, and 32.3% were taking them at the time of the survey. They took supplements primarily for aesthetic reasons (e.g., hair and skin health) and preferred purchasing supplements at pharmacies. Nearly all (89.9%) participants could define supplements correctly, and 43.6% reported that supplements improved health. More than half the sample believed that supplements are safe. While a large proportion of participants correctly identified the recommended number of daily servings of fruits and vegetables, relatively few actually consumed that recommended amount. More than one-third of participants consumed more than one type of supplement simultaneously, and more than half reported that they would use supplements when necessary in the future. The results of this study suggest a need for long-term studies on the consumption of nutritional supplements among Saudis and its impact on health
External Evaluation of the Origin and Scale of the International Terrestrial Reference Frame
No full textImpact of the Network Effect on the Origin and Scale: Case Study of Satellite Laser Ranging
No full textITRF2008 plate motion model
No full textInternational audienceThe ITRF2008 velocity field is demonstrated to be of higher quality and more precise than past ITRF solutions. We estimated an absolute tectonic plate motion model made up of 14 major plates, using velocities of 206 sites of high geodetic quality (far from plate boundaries, deformation zones and Glacial Isostatic Adjustment (GIA) regions), derived from and consistent with ITRF2008. The precision of the estimated model is evaluated to be at the level of 0.3 mm/a WRMS. No GIA corrections were applied to site velocities prior to estimating plate rotation poles, as our selected sites are outside the Fennoscandia regions where the GIA models we tested are performing reasonably well, and far from GIA areas where the models would degrade the fit (Antarctica and North America). Our selected velocity field has small origin rate bias components following the three axis (X, Y, Z), respectively 0.41 ± 0.54, 0.22 ± 0.64 and 0.41 ± 0.60 (95 per cent confidence limits). Comparing our model to NNR-NUVEL-1A and the newly available NNR-MORVEL56, we found better agreement with NNR-MORVEL56 than with NNR-NUVEL-1A for all plates, except for Australia where we observe an average residual rotation rate of 4 mm/a. Using our selection of sites, we found large global X-rotation rates between the two models (0.016°/Ma) and between our model and NNR-MORVEL56 of 0.023°/Ma, equivalent to 2.5 mm/a at the Earth surface
Test of insulin resistance in nondiabetic and streptozotocin-induced diabetic rats using glycosylated hemoglobin test and other interventions
No full textType 2 diabetes is common globally. Pioglitazone (PGZ) is an oral TZD antidiabetic, whereas chromium-picolinate (Cr-PL) and Cr-glucose tolerance factor (Cr-GTF) are useful type 2 diabetes mellitus (T2DM) supplements. Cr-PL/GTF antioxidants cure T2DM. They may fail in diabetes with or without insulin-sensitizing medications. It examined how Cr-PL, Cr-GTF, PGZ, and their combination affected glucose, glycosylated hemoglobin, insulin, and HOMA-IR. Sixty-three adult Sprague-Dawley rats (220–300 g) were selected, and nine rats were randomly assigned to a normal nondiabetic group. In contrast, 54 rats were randomly split into 9 rats per each of the 6 major groups and injected intraperitoneally with 40 mg/kg STZ to induce T2DM. Rats were administered PGZ = 0.65 mg/kg (rat weight)/day, Cr-PL = 1 mg/kg, Cr-GTF = 1 mg/kg, and their combinations (PGZ + Cr-PL and Cr-GTF) daily for 6 weeks per intervention. The PGZ + Cr-PL and PGZ + Cr-GTF groups had substantially lower insulin levels than the PGZ group (13.38 ± 0.06, 12.98 ± 0.19 vs. 14.11 ± 0.02, respectively), with the PGZ + Cr-GTF group having the lowest insulin levels (12.98 ± 0.19 vs. 14.11 ± 0.02, 13.38±0.06, respectively). Intervention substantially reduced HOMA-IR in the PZ + Cr-PL and PZ + Cr-GTF groups compared to PGZ (7.49 ± 0.04, 6.69 ± 0.11 vs. 8.37 ± 0.04, respectively). This research found that combining PGZ with Cr-GTF resulted in considerably lower HOMA-IR levels than the PGZ and Cr-PL groups (6.69 ± 0.11 vs. 8.37 ± 0.04, 7.49 ± 0.04, respectively). Both Cr-PL and Cr-GTF may control T2DM. Both Cr complexes improved T2DM biomarkers more than the control diabetic group without medication. PGZ alone and PGZ + Cr-PL had less pharmacological synergy than Cr-GTF and PGZ in altering insulin and HOMA-IR blood levels. These encouraging discoveries need more study
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