Deterministic polarization chaos from a laser diode

Fifty years after the invention of the laser diode and fourty years after the report of the butterfly effect - i.e. the unpredictability of deterministic chaos, it is said that a laser diode behaves like a damped nonlinear oscillator. Hence no chaos can be generated unless with additional forcing or parameter modulation. Here we report the first counter-example of a free-running laser diode generating chaos. The underlying physics is a nonlinear coupling between two elliptically polarized modes in a vertical-cavity surface-emitting laser. We identify chaos in experimental time-series and show theoretically the bifurcations leading to single- and double-scroll attractors with characteristics similar to Lorenz chaos. The reported polarization chaos resembles at first sight a noise-driven mode hopping but shows opposite statistical properties. Our findings open up new research areas that combine the high speed performances of microcavity lasers with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure

Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic

Ape Conservation Physiology: Fecal Glucocorticoid Responses in Wild Pongo pygmaeus morio following Human Visitation

Nature-based tourism can generate important revenue to support conservation of biodiversity. However, constant exposure to tourists and subsequent chronic activation of stress responses can produce pathological effects, including impaired cognition, growth, reproduction, and immunity in the same animals we are interested in protecting. Utilizing fecal samples (N = 53) from 2 wild habituated orangutans (Pongo pygmaeus morio) (in addition to 26 fecal samples from 4 wild unhabituated orangutans) in the Lower Kinabatangan Wildlife Sanctuary of Sabah, Malaysian Borneo, we predicted that i) fecal glucocorticoid metabolite concentrations would be elevated on the day after tourist visitation (indicative of normal stress response to exposure to tourists on the previous day) compared to samples taken before or during tourist visitation in wild, habituated orangutans, and ii) that samples collected from habituated animals would have lower fecal glucocorticoid metabolites than unhabituated animals not used for tourism. Among the habituated animals used for tourism, fecal glucocorticoid metabolite levels were significantly elevated in samples collected the day after tourist visitation (indicative of elevated cortisol production on the previous day during tourist visitation). Fecal glucocorticoid metabolite levels were also lower in the habituated animals compared to their age-matched unhabituated counterparts. We conclude that the habituated animals used for this singular ecotourism project are not chronically stressed, unlike other species/populations with documented permanent alterations in stress responses. Animal temperament, species, the presence of coping/escape mechanisms, social confounders, and variation in amount of tourism may explain differences among previous experiments. Acute alterations in glucocorticoid measures in wildlife exposed to tourism must be interpreted conservatively. While permanently altered stress responses can be detrimental, preliminary results in these wild habituated orangutans suggest that low levels of predictable disturbance can likely result in low physiological impact on these animals

A comprehensive overview of radioguided surgery using gamma detection probe technology

The concept of radioguided surgery, which was first developed some 60 years ago, involves the use of a radiation detection probe system for the intraoperative detection of radionuclides. The use of gamma detection probe technology in radioguided surgery has tremendously expanded and has evolved into what is now considered an established discipline within the practice of surgery, revolutionizing the surgical management of many malignancies, including breast cancer, melanoma, and colorectal cancer, as well as the surgical management of parathyroid disease. The impact of radioguided surgery on the surgical management of cancer patients includes providing vital and real-time information to the surgeon regarding the location and extent of disease, as well as regarding the assessment of surgical resection margins. Additionally, it has allowed the surgeon to minimize the surgical invasiveness of many diagnostic and therapeutic procedures, while still maintaining maximum benefit to the cancer patient. In the current review, we have attempted to comprehensively evaluate the history, technical aspects, and clinical applications of radioguided surgery using gamma detection probe technology

Complications of central venous catheterization in critically ill children

WOS: 000249493400009PubMed ID: 17875082Background: Placement of central venous catheter is essential in the management of critically ill children. The purpose of the present paper was to evaluate the success rate, mechanical and thrombotic complications and risk factors associated with these complications from different central venous access sites in critically ill children. Methods: A prospective study was undertaken from February 2000 to March 2005 of 369 central venous catheterizations in children in a pediatric intensive care unit. Results: The veins most frequently used were femoral vein (45%), subclavian vein (32.2%), and internal jugular vein (22.8%). Mean +/- SD duration of catheterization was 9.5 +/- 6.5 days. The procedure was performed under emergency conditions in 18% of patients with an overall success rate of 92.4%. The success rate was significantly lower in younger patients with subclavian catheterization. Insertion-related complications were noted, including 33 arterial punctures (8.9%), 27 cases of malposition (7.3%), 19 hematomas (5.2%), 12 cases of minor bleeding (3.3%), and three cases of pneumothorax (0.8%), and they were more common in the subclavian vein than in the internal jugular and femoral vein. Multiple attempts and failed attempts significantly correlated with higher incidence of complications. Maintenance-related complications included obstruction (n = 26; 7%), accidental removal (n = 14; 3.8%), central venous thrombosis (n = 8; 2.2%), subcutaneous extravasation (n = 14; 3.8%), dislodgment (n = 1; 0.25%), and extravascular infusion (n = 1; 0.25%). The frequency of catheter maintenance-related complications was significantly higher in femoral catheterizations and increased significantly with an increase in the duration of catheterization. A total of five serious complications were seen (pneumothorax in three, dislodgment in one and extravascular infusion in one) in the present series. Conclusions: Central venous catheterization in critically ill children is a relatively safe procedure, with a 1.3% rate of serious complications and no mortality. It seems safer to choose initially the femoral or internal jugular vein instead of the subclavian vein because of high success rate without serious insertion-related complications