We present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ∼100 days. AT 2018cow rose over a few days to a peak luminosity Lpk ∼ 4 ...× 1044 erg s−1, exceeding that of superluminous supernovae (SNe), before declining as L ∝ t−2. Initial spectra at δt 15 days were mostly featureless and indicated large expansion velocities v ∼ 0.1c and temperatures reaching T ∼ 3 × 104 K. Later spectra revealed a persistent optically thick photosphere and the emergence of H and He emission features with v ∼ 4000 km s−1 with no evidence for ejecta cooling. Our broadband monitoring revealed a hard X-ray spectral component at E ≥ 10 keV, in addition to luminous and highly variable soft X-rays, with properties unprecedented among astronomical transients. An abrupt change in the X-ray decay rate and variability appears to accompany the change in optical spectral properties. AT 2018cow showed bright radio emission consistent with the interaction of a blast wave with vsh ∼ 0.1c with a dense environment ( for vw = 1000 km s−1). While these properties exclude 56Ni-powered transients, our multiwavelength analysis instead indicates that AT 2018cow harbored a "central engine," either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. The engine released ∼1050-1051.5 erg over ∼103-105 s and resides within low-mass fast-moving material with equatorial-polar density asymmetry (Mej,fast 0.3 M☉). Successful SNe from low-mass H-rich stars (like electron-capture SNe) or failed explosions from blue supergiants satisfy these constraints. Intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations.
A variety of patient positioning options exist on modern fracture tables for use during intramedullary nailing procedures. With the advent of interlocking and reconstruction nailing, some of these ...procedures can be complicated and prolonged. The use of the hemilithotomy position for prolonged intramedullary nailing procedures can result in the development of a compartment syndrome in the uninjured leg, no matter what type of suspension device is used for that leg. The occurrence of this iatrogenic injury in the patient's well leg can be devastating in light of the contralateral fracture. Two patients at this institution have had such a condition in the past two years, and the authors have revised their positioning procedures. Review of the surgical literature shows that this complication has been seen in urologic, gynecologic, and general surgical patients, but has not been widely reported in the orthopaedic population. Recommendations for avoiding this problem include the use of other positions or distraction devices when performing intramedullary nailings, or, when the hemilithotomy position cannot be avoided, early intraoperative repositioning of the leg when possible.
Titanium plates and screws have become widely used for the fixation of fractures and osteotomies. We began using them in 1992; however, several early hardware failure prompted a retrospective review ...of the occurrence of this complication. A 2-year time period was reviewed at two institutions with comparison of hardware failure rates using titanium and stainless steel implants. At one institution, 51 fractures or osteotomies of the long bones were fixed by the senior author using titanium implants between July 1992 and July 1994. One hundred one similar cases were treated over the same period by the same surgeon using stainless steel implants. The outcome is known for 48 of the cases performed with titanium and for 80 of the cases performed with stainless steel. There were five postoperative implant failures using titanium and one using stainless steel. Metallurgical analysis of one set of broken implants retrieved during a revision surgery showed no manufacturing defects. At the second institution, 21 titanium and 138 stainless steel platings were performed over 2 years. There were four titanium implant failures in four patients and one stainless steel implant failure. Our experience suggests that these implants should be used with care, particularly in high-demand settings such as nonunion or noncompliance, and that further research needs to be conducted to establish appropriate clinical indications for their usage.
We examined the effects of seed mass on seed survival and germination in the herbaceous perennial Coreopsis lanceolata (L.) (Asteraceae). Seeds were collected from bagged flower heads, weighed and ...sorted into mass classes. Seed mass variation was 29-fold (range 0.111 to 3.210 mg), almost twice as high as in other species. For seeds buried in soil flats 0, 1, 2, 3 and 4 cm, larger seeds had greater viability, emerged from lower depths, and had higher emergence rates. After 2-yr burial in nylon bags in the field, larger seeds had higher survivorship and viability rates but lower germination rates. The lower germination rates of large seeds after burial in the field may be due to dormancy. This study is the first to test seeds previously buried and recovered for survival, viability and germination. Seedmass variation may be maintained by differential dormancy and germination which results in spreading the risk of recruitment.
We examined physical and physiological factors that control germination in the herbaceous perennial, Coreopsis lanceolata L. (Asteraceae). Seeds stored in paper envelopes for 6 to 18 months at room ...temperature were tested for germination on moistened filter paper in petri dishes. Germination percentages were greatest at 15 and 25 C and 12 h light/dark cycles. Germination percentages of imbibed seeds were not affected by previous storage at -10 C. Imbibed seeds subjected to 5 C entered a secondary dormancy that could not be broken by subsequent warmer temperatures, light/dark cycles or freezing temperatures. This study is the first of which we are aware documenting secondary dormancy in a perennial species. Secondary dormancy in C. lanceolata may be a mechanism for spreading the risk of recruitment.
When the head rotates, vestibulocollic reflexes counteract the rotation by causing contraction of the neck muscles that pull against the imposed motion. With voluntary head rotations, these same ...muscles contract and assist the movement of the head. The purpose of this study was to determine if an infinite variety of muscle activation patterns are available to generate a particular head movement, of if the CNS selects a consistent and unique muscle pattern for the same head movement whether performed in a voluntary or reflex mode. The relationship of neck muscle activity to reflex and voluntary head movements was examined by recording intramuscular EMG activity from six neck muscles in three alert cats during sinusoidal head rotations about 24 vertical and horizontal axes. The cats were trained to voluntarily follow a water spout with their heads. Vestibulocollic reflex (VCR) responses were recorded in the same cats by rotating them in an equivalent set of planes with the head stabilized to the trunk so that only the vestibular labyrinths were stimulated. Gain and phase of the EMG responses were calculated, and data analyzed to determine the directions of rotation for which specific muscles produced their greatest EMG output. Each muscle exhibited preferential activation for a unique direction of rotation, and weak responses during rotations orthogonal to that preferred direction. The direction of maximal activation could differ for reflex and voluntary responses. Also, the best excitation of the muscle was not always in the direction that would produce a maximum mechanical advantage for the muscle based on its line of pull. The results of this study suggest that a unique pattern of activity is selected for VCR and tracking responses in any one animal. Patterns for the two behaviors differ, indicating that the CNS can generate movements in the same direction using different muscle patterns.
Electromyographic activity of dorsal neck muscles and neck torques was recorded to study vestibulocollic, cervicocollic, and combined reflexes in alert and decerebrate cats during rotations of the ...whole body, the body except for the head, and the head but not the rest of the body. Cats were rotated about many axes that lay in the frontal, sagittal, and horizontal planes using sinusoidal 0.25-Hz waveforms or sum-of-sinusoid wave-forms. Robust electromyographic responses were recorded from six muscles, with response directionality that in most cases did not show strong dependence on the reflex tested or on other factors including exact neck angle, stimulus amplitude from 5 degrees to 60 degrees, and intact versus decerebrate state. Based on the strength of responses to rotations about all the tested axes, neck muscles could be characterized by maximal activation direction vectors representing the axis and direction of rotation in three-dimensional space that was most excitatory during reflex responses. Responses to rotations about axes that lay in a coordinate plane were predicted by a cosine function of the angle between the axis under test and the maximally excitatory axis in the plane. All muscles were excited by the nose down phase of pitch rotation and by yaw and roll away from the side on which the muscle lay. Biventer cervicis was best activated by rotations with axes near nose-down pitch, and its axis of maximal activation also had small, approximately equal components of yaw and roll toward the contralateral side. Complexus was best excited by rotations with axes nearest roll, but with large components along all three axes. Occipitoscapularis was best excited by rotations about axes near pitch, but with a moderately large contralateral yaw component and a smaller but significant contralateral roll component. Splenius was best excited by rotations with a large component of contralateral yaw, considerable nose-down pitch, and a smaller component of contralateral roll. Rectus major was best excited by rotations near nose-down pitch, but with a substantial contralateral yaw component and smaller contralateral roll component. Obliquus inferior was best excited by rotations with a large component of contralateral yaw, but with considerable contralateral roll and nose-down pitch components. All muscles responded as though they received convergent input from all three semicircular canals. Vestibulocollic and combined reflex responses in alert cats and vestibulocollic, cervicocollic, and combined responses in decerebrate cats appeared to have the same directionality, as evidenced by insignificant shifts in maximal activation vectors.
The vestibulo-ocular and vestibulo-collic reflexes are well-studied sensorimotor systems with dynamic properties that have been successfully modeled. Recently proposed matrix and tensorial models ...attempt to describe the spatial organization of these reflexes in three dimensions. Here we describe experiments that test these models. We show that a matrix model of the vestibulo-ocular reflex provides a satisfactory description of its spatial properties. The vestibulo-collic reflex is more complex, but a tensorial model makes close predictions of neck muscle excitation by the vestibulo-collic reflex. In addition, our preliminary data show that the cervico-collic or neck stretch reflex produces essentially the same spatial pattern of neck muscle excitation as the vestibulo-collic reflex, a finding predicted by the tensorial model. We conclude by showing electromyographic and single neuron responses that can be modeled only by combining models of dynamics with models of spatial organization. We believe that the development of such models is the next major challenge in the application of quantitative methods to analysis of reflex behavior.
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