Remarkable similarities of two pairs of stable and saddle canards in a van der Pol oscillator under extremely weak periodic perturbation

Canards are interesting nonlinear phenomena that have generated intense research interest since their discovery in the late 20th century. We are interested here in how canard-generating dynamics are influenced by extremely weak periodic perturbations that cause the formation of saddle-node bifurcations in the fundamental harmonic entrainment region. In a previous study, we discovered that another entrainment region exists within the fundamental harmonic entrainment region surrounded by the second saddle-node bifurcation curves. We found that two pairs of stable and saddle canards coexist in this second entrainment region under such weak periodic perturbation. Moreover, the stable and saddle canards are matched pairwise; i.e., each stable canard quite closely resembles a corresponding saddle canard. Calculation of the correlation coefficients of the four canards revealed two similar solutions on the order of 0.9999⋯ between the two pairs of similar canards. In contrast, the correlation coefficients of the dissimilar canards differ from unity in proportion to the difference between the given bifurcation parameter value and the parameter values at the saddle-node bifurcation points. Approximately, they take values from 0.998 to 0.975. These contrasts are noteworthy. Similar bifurcation phenomena were observed in the 1/2-subharmonic entrainment region. We hypothesize that the two pairs of stable and saddle canards are invariant with respect to a slight shift of time at the saddle-node bifurcation points, and we numerically prove that such a property approximately holds at the bifurcation points

A fully planar solar pumped laser based on a luminescent solar collector

A solar-pumped laser (SPL) that converts sunlight directly into a coherent and intense laser beam generally requires a large concentrating lens and precise solar tracking, thereby limiting its potential utility. Here, we demonstrate a fully-planar SPL without a lens or solar tracking. A Nd3+-doped silica fiber is coiled into a cylindrical chamber filled with a sensitizer solution, which acts as a luminescent solar collector. The body of the chamber is highly reflective while the top window is a dichroic mirror that transmits incoming sunlight and traps the fluorescence emitted by the sensitizer. The laser-oscillation threshold was reached at a natural sunlight illumination of 60% on the top window. Calculations indicated that a solar-to-laser power-conversion efficiency could eventually reach 8%. Such an SPL has potential applications in long-term renewable-energy storage or decentralised power supplies for electric vehicles and Internet-of-Things devices

Successful management of preoperatively diagnosed torsion of a subserosal uterine fibroid by pneumoperitoneum laparoscopic single-port surgery

Objective: Preoperative diagnosis and successful management of acute torsion of a subserosal fibroid by using appropriate imaging modalities and single-port laparoscopic surgery. Case report: A 44-year-old nulliparous woman presented with lower abdominal pain. Computed tomography and magnetic resonance imaging with contrast enhancement revealed a tumor in the pouch of Douglas with a low contrast at the center and thin-rim enhancement. Torsion of a uterine subserosal fibroid was diagnosed preoperatively. Laparoscopic single-port surgery by pneumoperitoneum was performed. Torsion of the pedicle attached to the uterine wall was excised by bipolar coagulation and cut with scissors. The extirpated fibroid was extracted from the umbilical wound. The pneumoperitoneum single-port laparoscopic surgery was completed as a gynecologic emergency operation. Conclusion: Torsional uterine fibroids are difficult to diagnose preoperatively as symptoms are nonspecific and need emergent surgical management as an acute abdomen. Preoperative diagnosis using appropriate imaging modalities is important to perform single-port laparoscopic surgery

Malignant transformation arising from mature cystic teratoma of the ovary presenting as ovarian torsion: a case report and literature review

Objective: Ovarian torsion is an acute gynecological condition. Torsion is more likely to occur with benign rather than malignant tumors. Mature cystic teratoma of the ovary (MCTO) is frequent in women of reproductive age; however, the incidence of malignant transformation is approximately 2%. We report a case of malignant transformation of MCTO presenting as ovarian tumor torsion. Case report: A 51-year-old premenopausal woman was diagnosed with mature cystic teratoma in the left ovary 7 years ago. The patient visited our hospital because she had been experiencing of pain in left lower abdomen for the past two days. She was diagnosed with ovarian tumor torsion and underwent emergency surgery. The left ovarian tumor was twisted, and left salpingo-oophorectomy was performed. Histopathological examination revealed squamous cell carcinoma arising from the MCTO. We carefully followed the patients without performing staging laparotomy. On postoperative day 112, multiple lymph node metastases in the pelvic and para-aortic areas were found by positron-emission tomography and computed tomography. After referral to a university hospital, total hysterectomy, right salpingo-oophorectomy, partial omentectomy, and pelvic and paraaortic lymphadenectomy were performed. Metastases of squamous cell carcinoma were confirmed in the pelvic and para-aortic lymph nodes. Six courses of adjuvant chemotherapy with paclitaxel and carboplatin were given following radical surgery to prevent the recurrence of malignant transformation of MCTO. No recurrence of the disease has been observed during 2 years of follow-up. Conclusio: When physicians diagnose large ovarian tumor torsion cases, preoperative examinations should be performed, with the possibility of malignancy in mind