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Search Results: 1 - 10 of 469 matches for " Twins Paradox "
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The Twins Clock Paradox History and Perspectives  [PDF]
Robert L. Shuler Jr.
Journal of Modern Physics (JMP) , 2014, DOI: 10.4236/jmp.2014.512108
Abstract:

The twins or clock paradox has been a subject of lively discussion and occasional disagreement among both relativists and the public for over 100 years, and continues to attract physicists who write papers giving new analyses or defending old ones, even though many physicists now consider the matter only of educational interest. This paper investigates the number of papers, which is increasing, and trends in explanations, some of which are now targeted at professional physicists and other of which are targeted at optical or radar visualization rather than problem solving. Observations of students indicate that the latest techniques help but only somewhat. An analysis is made of 21 previous treatments appearing in the education related American Journal of Physics, Einstein’s discussions and several other pedagogical papers. A new memory aid for simultaneity transformation is given that puts it on a par with “time dilation” and “length contraction” for quick and easy problem visualization. The point of view of a trailing twin is introduced to show how simultaneity changes account for missing time in the turnaround. Length contraction is treated on equal footing with time dilation, and Swann’s insight into clocks is extended to lengths. Treatments using the conventionality of simultaneity are seen as equivalent to choice of co-moving frames. Responses to difficult questions are suggested which avoid being dismissive, and engage students’ critical thinking.

Twin gestation: Is induction of labor possible in highly selected cases?  [PDF]
R. E. Mbu, J. Fouedjio, Y. Fouelifack, J. T. Ngo Batta, F. N. Tumasang, S. N. Ako, R. N. Tonye, M. B. Mbu, R. J. I. Leke
Open Journal of Obstetrics and Gynecology (OJOG) , 2012, DOI: 10.4236/ojog.2012.23043
Abstract: Induction of labor has been in practice for several decades but the decision to induce labor in multifetal gestations has not been accepted by many practitioners in contemporary obstetrics. The aim of this study was to compare maternal and fetal outcomes among women with uncomplicated twin gestations who were induced at term and those who were not. It was a cross-sectional analytic study that lasted ten years, (1st January 2000 to 31st December 2009 inclusive) at the maternity of the central hospital, Yaounde, Cameroon. 158 women were enrolled, 79 were induced and 79 went into labor spontaneously. Maternal and fetal outcomes, duration of labor, the prevalence of caesarean section were compared in the two groups. The average age of the women in the groups was 26, 75 ± 3.65 years (range 15 - 41 years). For those who were induced, indication was premature rupture of membranes in 44 (56%) of cases. The characteristics of induced and none induced women were similar, except for the number of antenatal consultations (P ≤ 0.001). There was a significant difference in the duration of labor in the two groups (6 hrs versus 9, 75 hrs; P ≤ 0.001). The overall rate of vaginal delivery in the two groups was 87, 97% (n = 139), 88.87% in the group that was induced versus 86.07% in the group that labor was spontaneous (OR 1, 22; 95% IC 0, 51-2, 92; p ≤ 0.90). With respect to primary outcomes, there were no statistically significant differences between the group that labor was induced and that which labor was spontaneous. The prevalence of caesarean delivery was similar in the two groups (10%, 12% vs 13%, 92%; OR 0%, 7%; 95% IC 0, 27-1, 85; P ≤ 0.50). The main indications for caesarean section were acute fetal distress and failed induction. The first and fifth minute APGAR scores less than 7 in the first twins delivered in the two groups were similar. The 312 children delivered in both arms did not show any complications at birth. However, there were 3 neonatal deaths (1 vs 2). There were no cases of uterine rupture or maternal deaths among the 156 women. Induction of labor may be proposed to women with uncomplicated term twin gestations with specific indications. Induction in these highly selected cases does not impute any additional risks but close monitoring of labor is very necessary.
Radial Electric Field in Tokamak Plasmas as a Physical Consequence of Ehrenfest’s Paradox  [PDF]
Romannikov Alexander
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.330201
Abstract: A simplified form and some possible theoretical resolutions of the so-called Ehrenfest’s Paradox are described. A relation between physical consequences of this relativistic paradox and charge density ρ of tokamak plasma is shown. Plasma experiments which could resolve the Ehrenfest’s Paradox are presented.
Comment on a Paper: “Ben-Naim’s ‘Pitfalls’: Don Quixote’s Windmill”, by Y. Fang, Open Journal of Biophysics, 2013, 3, 13-21  [PDF]
Arieh Ben-Naim
Open Journal of Biophysics (OJBIPHY) , 2013, DOI: 10.4236/ojbiphy.2013.34032
Abstract:

This article is a response to Fangs article which criticizes statements never made by Ben-Naim and never appeared in the literature.

Mullerian Agenesis in One of the Non-Identical Twins: A Case Report and Literature Review  [PDF]
Shweta Thapa K. C., Cunjian Yi
Yangtze Medicine (YM) , 2018, DOI: 10.4236/ym.2018.22009
Abstract: Mullerin agenesis also referred as mullerian aplasia, Mayer-Rokitansky-Kuster-Hauser Syndrome (MRKH) or vaginal agenesis is the congenital anomaly of vertical fusion defect of mullerian system resulting in variable abnormalities of female reproductive tract with normal functioning ovaries. It is second most common cause of primary amenorrhea after gonadal agenesis. The occurrence of mullerian agenesis in twins is very rare. We present the case of one of the non-identical twins, 22 years female, with primary amenorrhea. Her elder twin sister had a normal female reproductive system. In our case, diagnosis was supported by presence of definitive primary amenorrhea with well-developed secondary sexual characteristics. Normal physiological hormonal levels ruled out the ovarian or pituitary pathology. Imaging studies like ultrasonography and magnetic resonance imaging (MRI) provided additional confirmation.
Ischiopagus tetrapus conjoined twins: 22 years after separation
Chatterjee Subir,Chakravarty Amal,Demajumdar N,Sarkar Kalyan
Journal of Indian Association of Pediatric Surgeons , 2009,
Abstract: There is no record of both separated ischiopagus tetrapus conjoined twins leading normal lives 22 years after separation. We separated a pair of such twins in 1986 and have followed them up till date. Details regarding the technique of separation and the procedures required to ensure normal defecation and micturition and normal musculoskeletal function have been described by us in earlier communications. In this paper we describe their present status and ability to face the world as independent adult females. The outcome reflects the responsibilities and dedication of pediatric surgeons for infant patients with congenital problems after they have become adults, taking a pivotal role to involve surgeons of other disciplines as and when necessary.
Conjoined Twins: The Flip Side
Tayyaba Batool,Jamshed Akhtar
APSP Journal of Case Reports , 2010,
Abstract: We report a case of conjoined twins where many lateral issues influenced the management.
Parapagus dicephalus dibrachus dipus: A case of conjoined twins
Abdullah Karaer,?smail Tanr?kulu,Nedim Güne?,Ediz ?ak?r
Journal of the Turkish-German Gynecological Association , 2009,
Abstract: In this report, we describe the case of a woman with a prenatal diagnosis of parapagus dicephalus dibrachus dipus conjoined twins at 14-15 weeks of gestation via two-dimensional ultrasonography. The parents elected to terminate the pregnancy and the patient delivered a 15-cm 130-g male fetus. There were two heads and necks which appeared grossly normal. The thoracic and abdominal cavities were shared. The fetus had four normal limbs. On internal examination, there were two separate structurally normal hearts. There were two larynges and four lungs. Two esophagi fused to enter a single stomach. The diaphragm was common and separated a single abdominal cavity. Distally, the alimentary system including the liver and gallbladder was single.
On the So-Called Gibbs Paradox, and on the Real Paradox
Arieh Ben-Naim
Entropy , 2007, DOI: 10.3390/e9030133
Abstract: Two versions of the so-called Gibbs paradox are discussed. Both of these areshown to be non-paradoxes. It is also shown that there is a different real paradox that emergesfrom Gibbs writings.
Dynamic Electropulsing Induced Phase Transformations and Their Effects on Single Point Diamond Turning of AZ91 Alloy  [PDF]
Duo Zhang, S. To, Yaohua Zhu, Hao Wang, Guoyi Tang
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2012, DOI: 10.4236/jsemat.2012.21003
Abstract: The effects of dynamic electropulsing on microstructure changes and phase transformations of a rolled Mg-9Al-1Zn alloy were studied by using optical microscopy, X-ray diffraction, back-scattered scanning microscopy and transmission electron microscopy techniques. The decomposition of β phase was accelerated under dynamic electropulsing, compared with the conventional thermal processes. Dynamic electropulsing was less effective in affecting the phase transformations, but more effective in reducing residual stress than the static electropulsing. Dynamic electropulsing improved machinability of single point diamond turning, the mechanism of which is discussed from the point of view of dislocation dynamics.
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