Characterization of maximum hands-off control

Maximum hands-off control aims to maximize the length of time over which zero actuator values are applied to a system when executing specified control tasks. To tackle such problems, recent literature has investigated optimal control problems which penalize the size of the support of the control function and thereby lead to desired sparsity properties. This article gives the exact set of necessary conditions for a maximum hands-off optimal control problem using an $L_0$-(semi)norm, and also provides sufficient conditions for the optimality of such controls. Numerical example illustrates that adopting an $L_0$ cost leads to a sparse control, whereas an $L_1$-relaxation in singular problems leads to a non-sparse solution.Comment: 6 page

Rabi Oscillations in Landau-Quantized Graphene

We investigate the relation between the canonical model of quantum optics, the Jaynes-Cummings Hamiltonian and Dirac fermions in quantizing magnetic field. We demonstrate that Rabi oscillations are observable in the optical response of graphene, providing us with a transparent picture about the structure of optical transitions. While the longitudinal conductivity reveals chaotic Rabi oscillations, the Hall component measures coherent ones. This opens up the possibility of investigating a microscopic model of a few quantum objects in a macroscopic experiment with tunable parameters.Comment: 5 pages, 4 figure

Information Entropy in Cosmology

The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is identical to a fluid model of the `Kullback-Leibler Relative Information Entropy', expressing the distinguishability of the local inhomogeneous mass density field from its spatial average on arbitrary compact domains. We discuss the time-evolution of `effective information' and explore some implications. We conjecture that the information content of the Universe -- measured by Relative Information Entropy of a cosmological model containing dust matter -- is increasing.Comment: LateX, PRLstyle, 4 pages; to appear in PR

A comparison of teres minor and infraspinatus muscle activation in the prone position

BackgroundThe electromyography (EMG) activity of the teres minor (TMi) and infraspinatus (IS) muscle has been demonstrated to vary depending on the arm position, such as in the coronal or scapular position, during intervention exercises. This may be reflected by different EMG activities demonstrated between the TMi and IS muscle during the acceleration and deceleration phases of the pitching motion. Tenderness in the scapular attachment site of the TMi muscle is often seen in baseball pitchers after pitching but not the attachment site of the IS muscle. However, few studies have investigated an interaction between TMi and IS muscle activity across different resistance exercises with different arm positions. The purpose of this study was to identify the feature of TMi and IS muscle activity in the presence of manual resistance applied in the prone position. MethodsEighteen collegiate baseball players volunteered their participation. Raw EMG amplitudes of the TMi, IS, posterior deltoid, middle deltoid, and upper trapezius muscles on the dominant shoulder were measured during intervention exercises. All subjects performed manual isometric resistance exercises: horizontal abduction (HABD) and external rotation (ER) of the glenohumeral joint with 40% of the manual maximum strength test in prone. The subjects also performed each of the HABD and ER resistance exercises with the arm actively positioned at 0° and 45° of ER of the glenohumeral joint in the coronal and scapular planes. ResultsBoth TMi and IS muscle activities significantly increased with the arm positioned at 45° of ER compared with 0° of ER regardless of the exercise (P \u3c .05). TMi activity was significantly greater with HABD resistance than IS muscle activity regardless of the arm positions, whereas it was significantly less with ER resistance than IS muscle activity. ConclusionThe findings of this study indicated that the TMi and IS muscles were most highly activated during the HABD resistance with the arm actively positioned at 45° of ER in the coronal plane. The results of this study have clinical implications regarding the careful selection of arm position in both exercise and clinical examination for the TMi and IS muscles

Can the Scapular Dyskinesis Test be Associated with Throwing Related Injuries During the Course of Collegiate Baseball Seasons?

Background A pattern of scapular dyskinesis on the dominant side has been demonstrated to be associated with a decrease in throwing arm conditions identified by a self-report outcome assessment in collegiate baseball pitchers during the course of a single season. However, it is unclear if symptomatic shoulders in baseball pitchers may be associated with the presence of scapular dyskinesis. Purpose To study the relationship between the presence of scapular dyskinesis and throwing-related injury in collegiate baseball pitchers during each respective course of up to four subsequent seasons. Methods A single Division 1 National Collegiate Athletic Association team participated in this study over a four-year-period. The scapular dyskinesis test was implemented during the preseason for baseball pitchers. Players were followed throughout each respective season to track the incidence of throwing-related upper extremity injuries. Results A total of 36 collegiate baseball pitchers (height: 185.3 ± 5.6 cm, weight: 88.8 ± 7.8 kg, age: 20.0 ± 1.5 years) consisting of 57 pitcher seasons were followed in this study, in which 18 pitchers remained with the team for more than one year. Twenty-seven of the 57 pitchers were classified as having scapular dyskinesis demonstrated at around 90° of shoulder flexion on the throwing side. Five injuries (13.2% of a total of 38 injuries) were diagnosed as throwing-related shoulder injuries during the course of the intercollegiate baseball seasons. Four of the five throwing-related shoulder injuries occurred in pitchers who had scapular dyskinesis on their dominant side. Consequently, the odds ratio was 5.04 for the collegiate pitchers with scapular dyskinesis on the throwing arm side associated with a throwing-related shoulder injury compared to those with no scapular dyskinesis (p = 0.16). No relationship was identified between scapular dyskinesis on the throwing arm side and throwing-related elbow injury. Eighty-one percent of the scapular dyskinesis test results were not changed on the throwing side from the previous to the following year for those 18 pitchers who were followed for more than one season, whereas 42.9% of the results remained unchanged on the non-throwing side. Conclusion The results suggest that collegiate baseball pitchers with dominant arm scapular dyskinesis likely are at increased risk of throwing-related shoulder injury. Level of evidence Level 2, Prospective Cohort Study

Electromyography activity of the teres minor muscle with varying positions of horizontal abduction in the quadruped position

BackgroundThe teres minor (TMi) muscle exposed relatively high activity during the acceleration and deceleration phases of the throwing motion, compared with the infraspinatus muscle. However, few studies have identified TMi muscle activity in intervention exercises. The purpose of this study was to investigate TMi muscle activities in different horizontal adduction positions in the quadruped horizontal abduction exercise. This study hypothesized that TMi muscle activity would differ in response to resistance application across different horizontal adduction positions. Materials and methodsNineteen collegiate baseball players volunteered their participation. Raw electromyography activity of the TMi muscle along with 7 different muscles attached to the scapula on the dominant-side were collected, and normalized by each of the corresponding maximum voluntary isometric contractions. All subjects performed manual isometric resistance horizontal abduction exercises at 90° and 135° of abduction with 3 horizontal adduction angles in the quadruped position: 1) coronal, 2) scapular, and 3) sagittal plane. Electromyography data were also collected from rhythmical concentric contraction of horizontal abduction at 90° of abduction in the quadruped position. ResultsTMi muscle activity was significantly greater with the arm positioned in the coronal plane than that of the scapular and sagittal planes (41, 26, and 17% maximum voluntary isometric contraction, respectively) (P \u3c .05). ConclusionThe present study demonstrated that TMi muscle activity varied depending on horizontal adduction positions