Flat Trajectory Research Articles

Optimized Launch of a Rocket Launcher Type, From La Guajira - Colombia

The initial process for introducing the respective input variables to the mathematical models depends on the flight mission to define; keeping in mind the simplifications that are taking place are also established; as well as input data relevant to mention such as for example are the speed, the height, the cut-off, data concerning the orbit perigee, apogee, period and flat trajectory of the orbit. It is defined in the same simplified manner, the orbital elements and the inclination to consider. Additionally, the energy requirement is established and a specific impulse not defined, specific current pulses propellants either solid or liquid. Specific impulses of current propellants either solid or liquid must not exceed the limits established in technologically optimum mass distribution and the number of stages. At that point the main problem to observe will be associated with the number one phase in which we must find the path from the launch point to the injection of the payload, minimizing the loss of thrust required for acceleration, gravitational effects and drag. This requires a path to minimize these losses and minimize the overall fuel consumption of the vehicle. as part of the origin of the proposed research problem, was noted the work developed in the research hotbed SE-AST (Hotbed of astronautically studies) that have been developed academic work order relating to conceptual designs rocket dimensioning of motors and calculating orbits within the projects undertaken there labor and courses, but has been developed from work pending that address the dynamic of powered flight path.

Heterogeneity of sickness absence and disability pension trajectories among individuals with MS.

BackgroundThe variability of progression of multiple sclerosis (MS) suggests that MS is a heterogeneous entity.ObjectiveThe objective of this article is to determine whether sickness absence (SA) and disability pension (DP) could be used to identify groups of patients with different progression courses.MethodsWe analyzed mean-annual net months of SA/DP, five years prior to MS diagnosis, until the year of diagnosis, and five years after for 3543 individuals diagnosed 2003–2006, by modeling trajectory subgroups.ResultsFive different groups were identified, revealing substantial heterogeneity among MS patients. Before diagnosis, 74% had a flat trajectory, while the remaining had a sharply increasing degree of SA/DP. After diagnosis, 95% had a flat or marginally increasing trajectory, although at various SA/disability pension (DP) levels, whereas a small group of 5% had decreasing SA/DP. A majority had few or no SA/DP months throughout the 11-year study period. Higher age and a lower educational level were associated with an unfavorable trajectory (p values <0.01).ConclusionsThere’s a considerable heterogeneity of MS progression in terms of SA/DP. Compared with other measures of disability, sickness-absence and disability pension offer a continuous variable that can be assigned to every individual for each time period without missing data. To what extent the SA/DP measure reflects classical MS outcome-measures as well as how correlated it is with co-morbidities and working-conditions needs to be investigated further.

Population dynamics of walruses in Greenland

The historical and current dynamics of the three Atlantic walrus (Odobenus rosmarus rosmarus) populations that occur in Greenland are estimated using age- and sex-structured population models with exponential growth, density-regulated growth and selection-delayed dynamics. These models are integrated with data in a Bayesian framework, where the likelihood of the simulated population trajectories are evaluated from recent abundance estimates and age-structure information from a selective hunt. The overall decline in the Baffin Bay population caused by historical catches is unclear due to incomplete catch reporting prior to 1950s. However, it is estimated that the population declined by 40% from the 1960s to 2005; decreased catches (≈ 140 to ≈ 70) have subsequently allowed this population to increase. The 2012 abundance estimate is 1,400 (95% CI: 1,000-2,000) individuals, and the annual natural growth rate in this population is now 7.7% (95% CI: 6.7-8.9%). Averaging across models, it is estimated that West Greenland/Baffin Island walruses declined by 80% from 7,000 (95% CI: 5,400-10,000) in 1900 to 1,350 (CI: 950-1,950) in 1960. Hereafter they increased to 3,100 (95% CI: 2,500-4,400) in 1993, and owing to increased catches they have experienced a minor decline between 1994 and the early 2000s. Annual catches where then cut from 190 to the current quota of 61, and the population is again increasing with a 2012 estimate of 3,900 (95% CI: 2,500-5,300) individuals. A 2012 estimate of 1,400 (95% CI: 700-3,100) walruses in East Greenland is recovered relative to 1888; the year prior to our first historical catches by European sealers. The historical trajectory, however, is uncertain: Density regulation estimates a relatively flat trajectory, with a maximal depletion in 1890 to 80% of the initial abundance, and a slow continuous increase to almost no current growth. A recovered population is also estimated by selection-delayed dynamics. However, this model estimates a continued increase, and a historical depletion to 2% in 1957. These results are only partially comparable with an earlier assessment for East Greenland. Updated abundance estimates for West Greenland, and modelling with age-structured data from Baffin Bay, have greatly improved our status estimates for Baffin Bay and West Greenland/Baffin Island.

Center of mass mechanics of chimpanzee bipedal walking.

Center of mass (CoM) oscillations were documented for 81 bipedal walking strides of three chimpanzees. Full-stride ground reaction forces were recorded as well as kinematic data to synchronize force to gait events and to determine speed. Despite being a bent-hip, bent-knee (BHBK) gait, chimpanzee walking uses pendulum-like motion with vertical oscillations of the CoM that are similar in pattern and relative magnitude to those of humans. Maximum height is achieved during single support and minimum height during double support. The mediolateral oscillations of the CoM are more pronounced relative to stature than in human walking when compared at the same Froude speed. Despite the pendular nature of chimpanzee bipedalism, energy recoveries from exchanges of kinetic and potential energies are low on average and highly variable. This variability is probably related to the poor phasic coordination of energy fluctuations in these facultatively bipedal animals. The work on the CoM per unit mass and distance (mechanical cost of transport) is higher than that in humans, but lower than that in bipedally walking monkeys and gibbons. The pronounced side sway is not passive, but constitutes 10% of the total work of lifting and accelerating the CoM. CoM oscillations of bipedally walking chimpanzees are distinctly different from those of BHBK gait of humans with a flat trajectory, but this is often described as "chimpanzee-like" walking. Human BHBK gait is a poor model for chimpanzee bipedal walking and offers limited insights for reconstructing early hominin gait evolution.

Trajectories of performance status decline in advanced cancer.

100 Background: Historically, functional decline is considered to occur steadily and inexorably in the last months of life, with a relatively steep trajectory compared to non-cancer patients (pts). As part of a trial evaluating the safety and clinical impact of discontinuing statin medications for patients in the palliative care setting, we recorded the performance status (PS) in 186 cancer patients regularly during their time on study and compared changes among those with differing baseline PS levels and between those with and without cancer. Methods: This was a multi-center, parallel-group, unblinded pragmatic trial. Eligibility included: age &gt; 18; life expectancy between 1 month and 1 year, on a statin for ≥ 3 months for primary or secondary prevention, recent deterioration in PS and no recent active cardiovascular disease. Participants, randomized to either discontinue or continue statins, were followed monthly for up to 1 year. Outcomes included survival, cardiovascular events, and PS. PS was measured using the Australia-modified Karnofsky Performance Status (AKPS) scale and grouped into 4 categories: AKPS=70, 60; 50 and 0-40. The trajectory of PS decline for each group was modeled using a piecewise-linear function allowing for knots at 4, 8, and 12 weeks and separated out between those participants who died and did not die during their time on study. A mixed model was used allowing for a random intercept for each participant. Results: Among the 186 subjects whose primary diagnosis was cancer, 111 died; among 195 without cancer, 75 died. Those who did not die maintained a relatively flat trajectory of AKPS across 20 weeks; for those who did die, AKPS scores declined somewhat over 20 weeks but this decline was most remarkable among those with a starting AKPS of 0-40. Compared to noncancer patients who died during the study period, PS levels were higher at baseline and had initially greater rates of decline. Conclusions: For advanced cancer patients, PS declines are less dramatic than previous estimates have suggested except for those with AKPS 0-40, suggesting precipitous declines at the very end of life for those with higher initial AKPS. Compared to noncancer patients, PS decline is slightly steeper among cancer pts.

Flight stability of a dual-spin projectile with canards

The concept of roll-decoupled course correction fuze with canards can provide a cost-effective solution to improve the delivery accuracy for conventional unguided ammunitions. Due to the dual-spin configuration and canards for such a projectile, the basic projectile stability theory should be extended to well perceive its behavior of motion. The seven degree-of-freedom dynamic equations of motion for the dual-spin projectile are established in the fixed-plane frame and the differential equation for the complex angle of attack is derived by the use of the projectile linear theory without the assumption of a flat trajectory. A revised stability criterion is established according to the Hurwitz stability criterion and analytic solutions of the stability boundaries for trim angles are developed. The new stability criterion can account for the possible flight instability of projectiles subjected to side forces applied at the nose, and can be reduced to the same form as the conventional spin-stabilized projectile case. Moreover, detailed trajectory simulations of two sample projectiles indicate that the new stability criterion gives satisfactory agreement with numerical results.

Unique solar flare of September 22, 2011: The suction effect

The specific features in the development of an X1 solar flare, which occurred on September 22, 2011, and was registered with the Atmospheric Imaging Assembly (AIA) device onboard the Solar Dynamics Observatory (SDO) in the UV line (λ = 304 A, He II), are analyzed. During the flare, which lasted about 12 h, cold plasma was sucked up with an increasing velocity from a very distant region into the low-lying hot region of flare energy release along a flat helical trajectory. This phenomenon fundamentally differs from a surge ejection, when matter previously ejected from the flare region returns to the flare hot zone under the action of gravity. Suction of cold plasma “from outside” into the hot flare region is interpreted in the scope of the rope flare mechanism, according to which an extremely inhomogeneous plasma density distribution in the cross-section originates in an emerging magnetic rope. In the region with a sharply decreased density (which is the suction region), the drift velocity in the current chanel can reach the ion thermal velocity, which inevitably results in the excitation of plasma turbulence and anomalous resistance, i.e., in the development of a flare.

Trajectories of Recurring Victimization Among People With Major Mental Disorders

Relatively little is known about the violent victimization experiences of people with major mental disorders. Moreover, to date, no studies have examined recurring violent victimization experiences of people with major mental disorders. Using a risk heterogeneity framework commonly used in the study of recurring victimization, the current study examines the extent of recurring victimization among people with Diagnostic and Statistical Manual of Mental Disorders (DSM) Axis I mental disorders and trajectories of recurring violent victimization (n = 262), across four waves of data collected during a 1-year longitudinal study. Multilevel logistic regression analyses tested disorder, time, and time by disorder cross-level interactions predicting recurring victimization. Results suggest that recurring violent victimization is not uncommon among mentally disordered victims of violence, with 64% of victims experiencing a recurring victimization at a later point in time. However, trajectories of recurring violent victimization are not uniform across types of mental illness. Indeed, individuals diagnosed with a substance abuse disorder or major depression show significantly declining trajectories across the follow-up period whereas individuals diagnosed with a manic disorder or a schizophrenia spectrum disorder have flat trajectories of recurring violent victimization across the study period. Results of tests for cross-level interactions between disorder type and time demonstrate that individuals with a major depression or substance abuse/dependence diagnosis are significantly different from those with a schizophrenia spectrum diagnosis in their trajectories of recurring victimization.

Receding horizon flight control for trajectory tracking of autonomous aerial vehicles

This paper addresses the implementation of a predictive control strategy for Unmanned Air Vehicles in the presence of bounded disturbances. The goal is to prove the feasibility of such a real-time optimization-based control design and to demonstrate its tracking capabilities for the nonlinear dynamics with respect to a reference trajectory which is pre-specified via differential flatness. In order to benefit from the computational advantages of the linear predictive control formulations, an off-line linearization strategy of the nonlinear model of the vehicle along the flat trajectory is employed. The proposed method exhibits effective performance validated through software-in-the-loop simulations and real flight tests on different Unmanned Aerial Vehicles (UAVs).

How time and perceptions of social context shape employee absenteeism trajectories

Although the impact of social influence on employee absenteeism is well established, almost nothing is known about the dynamic, temporal accrual of this influence. Latent growth modeling was used to trace absenteeism trajectories over 4years for employees who differed in years of organizational tenure. As expected, higher-tenure employees exhibited flat trajectories while those with lower tenure (1–3years) gradually increased their absenteeism to conform to the dominant norm of the organization. However, as predicted by theories of identification and social exchange, perceptions of social context moderated the latter effect. The more positive an employee's perceptions of top management, the lower his or her rate of increase in absenteeism. The more positive an employee's perceptions of work colleagues, the higher his or her rate of increase in absenteeism. Perceptions of supervisors were unrelated to the rate of change. The study clarifies how employees learn and adapt to organizational absence cultures.

Minimum Detectable Concentration as a Function of Gamma Walkover Survey Technique

Gamma walkover surveys are often performed by swinging the radiation detector (e.g., a 2-inch by 2-inch sodium iodide) in a serpentine pattern at a near constant height above the ground surface. The objective is to survey an approximate 1-m swath with 100% coverage producing an equal probability of detecting contamination at any point along the swing. In reality, however, the detector height will vary slightly along the swing path, and in some cases the detector may follow a pendulum-like motion significantly reducing the detector response and increasing the minimum detectable concentration. This paper quantifies relative detector responses for fixed and variable height swing patterns and demonstrates negative impacts on the minimum detectable concentration. Minimum detectable concentrations are calculated for multiple contaminated surface areas (0.1, 1.0, 3, 10, and 30 m2), multiple contaminants (60Co, 137Cs, 241Am, and 226Ra), and two minimum heights (5 and 10 cm). Exposure rate estimates used in minimum detectable concentration calculations are produced using MicroShield™ v.7.02 (Grove Software, Inc., 4925 Boonsboro Road #257, Lynchberg, VA 24503) and MDCs are calculated as outlined in NUREG-1575. Results confirm a pendulum-like detector motion can significantly increase MDCs relative to a low flat trajectory, especially for small areas of elevated activity--up to a 47% difference is observed under worst-modeled conditions.

Transzygomatic Approach with Intraoperative Neuromonitoring for Resection of Middle Cranial Fossa Tumors

The authors reviewed the surgical experience and operative technique in a series of 11 patients with middle fossa tumors who underwent surgery using the transzygomatic approach and intraoperative neuromonitoring (IOM) at a single institution. This approach was applied to trigeminal schwannomas (n = 3), cavernous angiomas (n = 3), sphenoid wing meningiomas (n = 3), a petroclival meningioma (n = 1), and a hemangiopericytoma (n = 1). An osteotomy of the zygoma, a low-positioned frontotemporal craniotomy, removal of the remaining squamous temporal bone, and extradural drilling of the sphenoid wing made a flat trajectory to the skull base. Total resection was achieved in 9 of 11 patients. Significant motor pathway damage can be avoided using a change in motor-evoked potentials as an early warning sign. Four patients experienced cranial nerve palsies postoperatively, even though free-running electromyography of cranial nerves showed normal responses during the surgical procedure. A simple transzygomatic approach provides a wide surgical corridor for accessing the cavernous sinus, petrous apex, and subtemporal regions. Knowledge of the middle fossa structures is essential for anatomic orientation and avoiding injuries to neurovascular structures, although a neuronavigation system and IOM helps orient neurosurgeons.

Predictive Control for Autonomous Aerial Vehicles Trajectory Tracking

This paper addresses a predictive control strategy for Unmanned Air Vehicles in the presence of bounded disturbances. The goal is to guarantee tracking capabilities with respect to a reference trajectory which is pre-specified using the differential flatness formalism. Furthermore, an off-line linearization strategy of the nonlinear model of the vehicle along the flat trajectory is proposed. Since the reference trajectory is available beforehand, an optimization problem which minimizes the tracking error for the vehicle is formulated in a predictive control framework. The proposed method exhibits effective performance validated through software-in-the-loop simulations for the control of Unmanned Aerial Vehicles (UAVs).

Patterns of developmental change in infants' nighttime sleep awakenings from 6 through 36 months of age.

Nighttime sleep awakenings and infant and family characteristics were measured longitudinally in more than 1,200 infants when the infants were 6, 15, 24, and 36 months old. By 6 months of age, the majority of children slept through the night, awakening their mothers only about once or twice per week. However, not all children followed this predominant developmental pattern. Using growth mixture modeling, we identified 2 distinct developmental patterns. One group, labeled Sleepers, included 66% of the children. These children showed a flat trajectory of sleep awakenings from 6 through 36 months, with mothers reporting their infant awakening from sleep about 1 night per week. The second group, labeled Transitional Sleepers, included 34% of the infants. These children had 7 reported nights of awakenings per week at 6 months, dropping to 2 nights per week at 15 months and to 1 night per week by 24 months. Compared with Sleepers, Transitional Sleepers were more likely to be boys, score higher on the 6-month difficult temperament assessment, be breastfed at 6 and 15 months old, and have more depressed mothers at 6 months old. Using 2-group structural equation modeling, we examined individual differences at different points on the individual infants' sleep trajectories. For infants in both groups, reported sleep awakenings were associated with difficult temperament measured at 6 months, breastfeeding, infant illness, maternal depression, and greater maternal sensitivity. Infant-mother attachment measures were not related to these sleep awakenings.

Using latent trajectory analysis of residuals to detect response shift in general health among patients with multiple sclerosis article

Individuals experiencing a change in health may experience a response shift that may attenuate HRQoL change estimates. The objective of this study was to estimate the proportion of individuals with multiple sclerosis (MS) who experienced a response shift as detected by the Latent Trajectory of Residuals approach. Participants in the NARCOMS Registry were included if they responded to the general health (GH) question of the SF-12 in at least 3 surveys. Linear growth modeling was used to identify predictors of self-reported GH, and the residuals from this model were used to determine group-based trajectories. Dual trajectories of GH and a measure of disability (PDSS) were used to examine convergence in change patterns over time. A total of 1,566 individuals were included in this study. The predictive GH model explained 55% of the variance; 99.7% of subjects did not experience a response shift as indicated by flat trajectories, and 0.3% lowered their rating of health as compared to predicted indicating a potential response shift. Among 13% of subjects with flat trajectories of PDDS, 5% had GH decreasing most strongly showing some discordance between symptoms and GH. A lower percentage of individuals experienced response shift than previous research on smaller samples. These results may indicate the true absence of response shift, or may be limited by using a categorical outcome of GH, and GH predictors that may have also been amenable to response shift, which decreases the appropriateness of using the LTA approach. Future work will include the use of growth curve latent class analyses to assess response shift.

Twenty‐One‐Year Trends and Correlates of Pressure to Change Drinking

The vast majority of individuals with alcohol problems in the United States and elsewhere do not seek help. One policy response has been to encourage institutions such as criminal justice and social welfare systems to mandate treatment for individuals with alcohol problems (Addiction, 1997;92:1133). However, informal pressures to drink less from family and friends are far more common than institutional pressures mandating treatment (Addiction, 1996;91:643). The prevalence and correlates of these informal pressures have been minimally studied. This analysis used data from 5 Alcohol Research Group National Alcohol Surveys (NAS) collected at approximately 5-year intervals over a 21-year period (1984 to 2005, pooled N = 16,241) to describe the patterns of pressure that drinkers received during the past year from spouse, family, friends, physicians, police, and the workplace. The overall trend of pressure combining all 6 sources across all 5 NAS data sets indicated a decline. Frequent heavy drinking and alcohol-related harms also declined, and both were strong predictors of receiving pressure. Trends among different sources varied. In multivariate regression models, pressure from friends showed an increase. Pressure from spouse and family showed a relatively flat trajectory, with the exception of a spike in pressure from family in 1990. The trajectory of decreasing of pressure over time is most likely the result of decreases in heavy drinking and alcohol-related harm. Pressure was generally targeted toward higher risk drinkers, such as heavy drinkers and those reporting alcohol-related harm. However, demographic findings suggest that the social context of drinking might also be a determinant of receiving pressure. Additional studies should identify when pressure is associated with decreased drinking and increased help seeking.

Evaluating the Forecasting Performance of Commodity Futures Prices

Commodity futures prices are frequently criticized as being uninformative for forecasting purposes because (1) they seem to do no better than a random walk or an extrapolation of recent trends and (2) futures prices for commodities often trace out a relatively flat trajectory even though global demand is steadily increasing. In this paper, we attempt to shed light on these concerns by discussing the theoretical relationship between spot and futures prices for commodities and by evaluating the empirical forecasting performance of futures prices relative to some alternative benchmarks. The key results of our analysis are that futures prices have generally outperformed a random walk forecast, but not by a large margin, while both futures and a random walk noticeably outperform a simple extrapolation of recent trends (a random walk with drift). Importantly, however, futures prices, on average, outperform a random walk by a considerable margin when there is a sizeable difference between spot and futures prices.

Improving Individual Measurement of Postoperative Pain: The Pain Trajectory

The purpose of this study was to demonstrate a method for increasing the precision and information yield of postoperative pain assessment. We recorded pain intensity ratings over 6 days after surgery in 502 elective surgery patients and examined individual pain trajectories. A linear fit of an individual patient's scores defines a trajectory with two features: (1) the intercept or initial pain intensity; and (2) the slope, or rate of pain resolution. Three pain trajectory patterns emerged from examination of the pain trajectory slopes. Most patients (63% of the sample) demonstrated a negative slope trajectory characterized by a decline in pain intensity over days after surgery. Other patients (25% of the sample) demonstrated a flat trajectory with no meaningful change over 6 days from pain they reported initially. A third patient group (12% of the sample) had a positive slope trajectory in which pain scores increased over 6 days after surgery. Measures derived from individual pain trajectories yielded much lower standard errors of measurement and therefore had better measurement precision than did conventional pain assessment methods. Pain trajectory measures proved sufficiently precise to characterize pain patterns reliably in individual patients. Progress in acute pain management requires effective pain assessment. The acute pain trajectory quantifies rate of pain resolution as well as pain intensity. It affords more precise measurement than conventional pain assessment and can identify abnormal postoperative pain resolution.

Stepping Off the Hedonic Treadmill

Theorists have long maintained that people react to major life events but then eventually return to a setpoint of subjective well-being. Yet prior research is inconclusive regarding the extent of interindividual variability. Recent theoretical models suggest that there should be heterogeneity in long-term stress responding ( Bonanno, 2004 ; Muthén &amp; Muthén, 2000 ). To test this idea, we used latent growth mixture modeling to identify specific patterns of individual variation in response to three major life events (bereavement, divorce, and marriage). A four-class trajectory solution provided the best fit for bereavement and marriage, while a three-class solution provided the best fit for divorce. Relevant covariates predicted trajectory class membership. The modal response across events was a relatively flat trajectory (i.e., no change). Nevertheless, some trajectories diverged sharply from the modal response. Despite the tendency to maintain preevent levels of SWB, there are multiple and often divergent trajectories in response to bereavement, divorce, and marriage, underscoring the essential role of individual differences.

ВАРИАНТ ТЕОРИИ УПРУГОПЛАСТИЧЕСКИХ ПРОЦЕССОВ И АППРОКСИМАЦИИ ФУНКЦИОНАЛОВ ПЛАСТИЧНОСТИ

A version of the theory of elastic-plastic processes and approximation of plasticity functionals is obtained on the basis of equations of the theory of elastic-plastic deformation related to the class of flow theories with combined hardening. The basic experiment and identification method for approximation parameters of plasticity functionals are formulated. Verification results of the version of the theory of elastic-plastic processes under complex loading by the flat trajectories of deformation are presented. Keywords: plasticity, complex loading, basic experiment, identification, verification.