Head Wind Research Articles

Formation rate of extreme mass ratio inspirals in active galactic nuclei

Extreme mass ratio inspirals (EMRIs) are important sources for space-borne gravitational wave detectors, such as the laser interferometer space antenna and TianQin. Previous EMRI rate studies have focused on the ``loss cone'' scenario, where stellar-mass black holes (sBHs) are scattered into highly eccentric orbits near the central massive black hole (MBH) via multibody interaction. In this work, we calculate the rate of EMRIs of an alternative formation channel: EMRI formation assisted by the accretion flow around accreting massive black holes. In this scenario, sBHs and stars on inclined orbits are captured by the accretion disk, and then subsequently migrate towards the MBH, under the influence of density wave generation and head wind. By solving the Fokker-Planck equation incorporating both sBH-sBH--sBH-star scatterings and sBH--star-disk interactions, we find that an accretion disk usually boosts the EMRI formation rate per individual MBH by $\mathcal{O}({10}^{1}--{10}^{3})$ compared with the canonical loss cone formation channel. Taking into account that the fraction of active Galactic nuclei (AGNs) is $\ensuremath{\sim}\mathcal{O}({10}^{\ensuremath{-}2}\ensuremath{-}{10}^{\ensuremath{-}1})$, where the MBHs are expected to be rapidly accreting, we expect EMRI formation assisted by AGN disks to be an important channel for all EMRIs observed by space-borne gravitational wave detectors. These two channels also predict distinct distributions of EMRI eccentricities and orbit inclinations with respect to the MBH spin equatorial plane, which can be tested by future gravitational wave observations.

Experimental study of a helicopter model in shipboard operations

The paper presents the experimental investigation of the aerodynamic interaction between a helicopter model and a ship model with a simplified geometry. In the first phase of the experiment, a series of wind tunnel tests were carried out in order to study the flow features on the flight deck for several wind conditions, without the presence of the helicopter. Pressure measurements and Particle Image Velocimetry surveys were performed to assess the effect of wind velocity and direction on the flow field in the landing region over the ship deck. Moreover, the effect of the Atmospheric Boundary Layer was investigated. In the second phase of the experimental campaign, a helicopter model was positioned in a series of points representative of a typical stern landing trajectory and a vertical descent above the landing spot. The landing maneuver was performed in three different wind conditions, including no-wind, head wind and wind blowing from port side of the deck. The rotor loads and moments were measured by means of a six-axis balance for all test points. The use of different measurement techniques in the present experiments provides a comprehensive database suitable for the study of the rotor-ship aerodynamic interaction. Additionally, the experimental results are used to develop an identification algorithm to be incorporated into the flight simulator environment to capture the effect of ship airwake on the rotor loads during shipboard operations.

CFD investigation of interaction effect between hull and accommodation on wind drag of a container ship in head wind

In this paper, we present a research on applying a commercial Computational Fluid Dynamics (CFD) code to determine interaction effect between hull and accommodation on wind drag of a container ship. For the high superstructure and large windward area ships such as container, wind drag acting on hull accounts for a large amount of total resistance. To clearly find aerodynamic performance and interaction effects on wind drag of a container ship, a full scale 1,200 TEU container has been used as a reference model. From results of comparison in the two computed cases of hull with and without accommodation, the interaction effects between hull and accommodation on aerodynamic performance and wind drag have been investigated. The targets of the paper has proposed a new solution to improve aerodynamic performances and reduce wind drag acting on the ship by reducing interaction effects between hull and accommodation.

The effect of optic flow cues on honeybee flight control in wind.

To minimize the risk of colliding with the ground or other obstacles, flying animals need to control both their ground speed and ground height. This task is particularly challenging in wind, where head winds require an animal to increase its airspeed to maintain a constant ground speed and tail winds may generate negative airspeeds, rendering flight more difficult to control. In this study, we investigate how head and tail winds affect flight control in the honeybee Apis mellifera, which is known to rely on the pattern of visual motion generated across the eye-known as optic flow-to maintain constant ground speeds and heights. We find that, when provided with both longitudinal and transverse optic flow cues (in or perpendicular to the direction of flight, respectively), honeybees maintain a constant ground speed but fly lower in head winds and higher in tail winds, a response that is also observed when longitudinal optic flow cues are minimized. When the transverse component of optic flow is minimized, or when all optic flow cues are minimized, the effect of wind on ground height is abolished. We propose that the regular sidewards oscillations that the bees make as they fly may be used to extract information about the distance to the ground, independently of the longitudinal optic flow that they use for ground speed control. This computationally simple strategy could have potential uses in the development of lightweight and robust systems for guiding autonomous flying vehicles in natural environments.

Model trajectories for a spinning tennis ball: III. The effect of a light wind on ground strokes

Theoretical models are presented for the trajectory of a rotating spherical projectile appropriate to the ground stroke in tennis, the ball being delivered in the presence of a light head wind, tail wind or side wind. The aim of the study is to determine, quantitatively, the amount of movement due to such light winds which are known to be present even in enclosed stadiums. The ball is assumed to be struck without spin (i.e., a ‘flat’ stroke), with top-spin or with under-spin (i.e., ‘slice’), with the ball being hit directly down the court or ‘cross-court’. Forces considered are the drag force, the lift force and gravity. It is found that a very modest wind can move the ball/court impact point by large amounts, of the order of tens of centimeters compared to the no-wind case. For example, a wind of 5 km h−1 (1.39 m s−1) may move the impact point by up to 1 m. The direction of movement of the impact point is, not surprisingly, normally in the direction to which the wind is blowing, although the exact direction depends, in-part, on the spin. An under-spun ball, for example, in the presence of a head wind can have its ‘range’ to the impact point actually increased, and in the presence of a tail wind the range can be decreased, a seemingly anomalous behaviour which at first sight seems surprising. Explanations for this behaviour are given. Actual movements due to the wind are compared with the product of the flight time and wind speed, since this quantity might be expected to provide an upper limit to such wind-induced movements. For a head or tail wind of 5 km h−1 and a 150 km h−1 full-court-length flat ground stroke with a flight time of 0.765 s, this product is 1.06 m and the shift in the impact point is 42.5% of this value, with larger shifts of up to 75% occurring for top-spin shots.

After all, it is an outdoor sport: Meta-analytic evidence for negative associations between wind compensation points and round scores in ski jumping competitions.

Wind conditions are well-known to affect results of ski jumping competitions. To alleviate effects of different head or tail winds and differences in inrun length due to jury or coaches’ decisions, the FIS (Féderation Internationale de Ski) has adopted a wind and gate compensation system since January 2010. However, the accuracy and fairness of the resulting compensation points are often questioned by athletes, spectators, and media commentators alike but have not yet been thoroughly investigated. In the present meta-analysis, we present evidence for systematic negative associations of wind points but positive associations of gate points with round scores across all World Cup and World Championship competitions of men in the ski jumping seasons 2016/2017 and 2017/2018 (k = 35 and 30, respectively). Moreover, our results indicate that absolute correlations between wind points and round scores increased in presence of larger wind point variability, thus indicating lower accuracy of compensation systems when conditions are more variable. Additionally, there was a trend for larger wind point malcompensations on larger jumping hills. Our results suggest that the current wind point compensation formula as well as gate factors should be reevaluated to prevent systematically biased point awards within and across competitions.

The history of transcatheter aortic valve implantation: The role and contribution of an early believer and adopter, the Netherlands.

This paper describes the history of transcatheter aortic valve implantation (TAVI) from its preclinical phase during which visionary pioneers developed its concept and prototype valves against strong head wind to first application in clinical practice (2002) and the clinical and scientific role of an early believer and adopter, the Netherlands (2005).

CBN Monetary Policy and Inflation Nexus in Nigeria: An empirical approach

Purpose: The study explored monetary policy effect on inflation stabilization in Nigeria. Increasing levels of indebtedness may have reduced the fiscal space for fiscal policy intervention and this leaves monetary policy as the real tool of choice for macroeconomic stabilisation. The question we need to ask then is, how effective is this tool of choice?Methodology: Monthly time series data from 2009-2018 were used in estimating the model. The ADF test for the stationarity, the johansen cointegration test and the vector error correction model were utilized in testing the variables. The findings from the unit root test did indicate stationarity at first difference 1(1). The cointegration (Johansen) test indicates that there was a nexus linking inflation and all the regressors adopted in the long term.Findings: The result of the VECM for the two estimated models shows a self-equilibrating mechanism of 14 per cent and 32 per cent for the first and second models respectively. The findings further reveal that the variables; liquidity ratio, policy rate (MPR), exchange rate, reserve requirement and treasury bills rate all had an effective impact on the inflation rate and that that effect was very significant. Hence, the CBN's monetary policy shocks do seem to have the expected traction on the Nigerian economy.Unique Contribution: The results make it pertinent for the CBN to utilize all the policy measures adopted in order to keep inflation within acceptable thresholds and prepare to keep inflation within the targeted range of 6-9 per cent, no matter the anticipated or unanticipated strong head winds.

Steady sailing performance of a ship in the proximity to the bank under windy conditions

This paper presents a method to efficiently calculate steady sailing conditions such as check helm, speed drop, hull drift angle, etc. of a ship moving in parallel to a bank wall under steady wind, together with the course stability at the equilibrium condition. Using this method, this study investigates the bank effect on the steady sailing condition and the course stability of a pure car carrier in steady wind and it evaluates the limiting wind condition for safe navigation (maneuvering limit). In case of head wind, a significant speed drop appears. In case of oblique head wind from the port side, the hull drift angle increases significantly and there is a distinct possibility that the ship touches the bank wall. In case of oblique following wind from the port side, the check helm increases significantly, because the wind force is added to the bank suction force. This becomes critical when the ship moves closer to the bank and in more shallow water areas, and the maneuvering limit level becomes more severe. The present method is a useful tool for measuring the maneuvering limit of a ship moving in close proximity to the bank under steady wind.

Reducing wind-induced vibrations of road sign structures through aerodynamic modifications: A computational pilot study for a practical example

In this article, we illustrate the potential of aerodynamic modifications of road signs to reduce wind-induced vibrations. Using a real-world sign structure operated by the Minnesota Department of Transportation, we focus on two modification variants, one based on the simple removal of secondary panels and one based on the addition of drag reducing rear extensions to the main panel. Our main analysis tool is a computational fluid dynamics framework based on the finite element method, which is validated against experiments with a scaled sign model that were conducted in the towing tank and the wind tunnel of the St. Anthony Falls Laboratory. We demonstrate computationally that aerodynamic modifications constitute an effective way of reducing the vibration amplitude in the example structure for head wind at the average operating wind speed. The present study can be seen as a first step towards establishing the use of aerodynamic devices for road sign structures.

Planetesimals in rarefied gas: wind erosion in slip flow

ABSTRACT A planetesimal moves through the gas of its protoplanetary disc where it experiences a head wind. Though the ambient pressure is low, this wind can erode and ultimately destroy the planetesimal if the flow is strong enough. For the first time, we observe wind erosion in ground-based and microgravity experiments at pressures relevant in protoplanetary discs, i.e. down to $10^{-1}\, \rm mbar$. We find that the required shear stress for erosion depends on the Knudsen number related to the grains at the surface. The critical shear stress to initiate erosion increases as particles become comparable to or larger than the mean free path of the gas molecules. This makes pebble pile planetesimals more stable at lower pressure. However, it does not save them as the experiments also show that the critical shear stress to initiate erosion is very low for sub-millimetre-sized grains.

The origin of tail-like structures around protoplanetary disks

Aims. We study the origin of tail-like structures recently detected around the disk of SU Aurigae and several FU Orionis-type stars. Methods. Dynamic protostellar disks featuring ejections of gaseous clumps and quiescent protoplanetary disks experiencing a close encounter with an intruder star were modeled using the numerical hydrodynamics code FEOSAD. Both the gas and dust dynamics were taken into account, including dust growth and mutual friction between the gas and dust components. Only plane-of-the-disk encounters were considered. Results. Ejected clumps produce a unique type of tail that is characterized by a bow-shock shape. Such tails originate from the supersonic motion of ejected clumps through the dense envelope that often surrounds young gravitationally unstable protostellar disks. The ejected clumps either sit at the head of the tail-like structure or disperse if their mass is insufficient to withstand the head wind of the envelope. On the other hand, close encounters with quiescent protoplanetary disks produce three types of the tail-like structure; we define these as pre-collisional, post-collisional, and spiral tails. These tails can in principle be distinguished from one another by particular features of the gas and dust flow in and around them. We find that the brown-dwarf-mass intruders do not capture circumintruder disks during the encounter, while the subsolar-mass intruders can acquire appreciable circumintruder disks with elevated dust-to-gas ratios, which can ease their observational detection. However, this is true only for prograde collisions; the retrograde intruders fail to collect appreciable amounts of gas or dust from the disk of the target. The mass of gas in the tail varies in the range 0.85–11.8 MJup, while the total mass of dust lies in the 1.75–30.1 M⊕ range, with the spiral tails featuring the highest masses. The predicted mass of dust in the model tail-like structures is therefore higher than what was inferred for similar structures in SU Aur, FU Ori, and Z CMa, making their observational detection feasible. Conclusions. Tail-like structures around protostellar and protoplanetary disks can be used to infer interesting phenomena such as clump ejection or close encounters. In particular, the bow-shock morphology of the tails could point to clump ejections as a possible formation mechanism. Further numerical and observational studies are needed to better understand the detectability and properties of the tails.

Predicting Low-Level Wind Shear Using 200-m-Resolution NWP at the Hong Kong International Airport

Abstract“Low-level wind shear” is a known aviation safety hazard and refers to a sustained change in head wind encountered by an aircraft during takeoff or landing. Because of their small spatiotemporal scales and high variability, automatic alerting of wind shears at airports around the world is almost exclusively detection based (using remote sensing equipment). Numerical modeling studies so far mainly cover individual cases and lack systematic validation. This paper presents the first statistical evaluation of numerical weather prediction (NWP) model performance in predicting low-level wind shear at a major international airport over a 2-yr continuous period. The 200-m-resolution Aviation Model (AVM) of the Hong Kong Observatory is used to generate runway-specific wind shear forecasts at 1-min output intervals for the Hong Kong International Airport (HKIA), known for its susceptibility to wind shear occurrence. The AVM forecasts are then validated against over 800 actual reports of wind shear by aircraft pilots over the two major arrival runway corridors, 07LA and 25RA, at HKIA between 2014 and 2015 using a verification scheme with the same level of spatiotemporal stringency as operational alerting systems at HKIA. With “relative operating characteristic” analysis, positive skill is consistently observed across both runway corridors throughout the study period and across all considered forecast lead times out to 6 h ahead. This study serves to establish and document the current capability of fine-resolution NWP in predicting the phenomenon of low-level wind shear for aviation weather applications.

Efficient Energy Conversion in Electrically Assisted Bicycles Using a Switched Reluctance Machine Under Torque Control

The prospect of physical exertion commonly acts as a deterrent to the adoption of cycling for everyday transport. A battery powered assistance torque electric motor could alleviate such physical exertion by reducing the effort required by the cyclist. This study investigates the potential effectiveness, efficiency, and energy saving of electrically-assisted cycling when assistance torque of a switched reluctance motor is designed to vary in accord to the cyclist instantaneous torque at the pedal cranks. Specifically, the modulated motor assistance torque is delivered at the least efficient human input torque points on the cycle. For a representative short distance cycling schedule modulating the instantaneous torque of the on-board electric motor causes the electric energy expenditure to not exceed that of the assisted cycling mode of an identical constant-torque motor. Furthermore, for the same speed profile cycling journey with added road gradient and head wind resistance, the energy expenditure of the modulated torque motor is equal to the constant torque motor. These findings indicate significant improvements in the cycling experience.

Effects of windscape on three-dimensional foraging behaviour in a wide-ranging marine predator, the northern gannet

Marine birds are strongly exposed to weather conditions at sea but to date, few studies have investigated the influences of wind or rainfall on their time-activity budgets or foraging routines. Here, we used data from GPS and pressure loggers to investigate the effects of wind speed and direction and rainfall on the 3-dimensional foraging behaviour of gannets Morus bassanus breeding at Bass Rock, Scotland. We found that birds spent more time actively foraging during stronger winds, but there was no subsequent increase in overall trip duration because individuals compensated by decreasing the time they spent on the water during stronger winds. Birds returned more quickly from distant foraging grounds, and those encountering head winds spent less time on the water and so were able to compensate to some extent for an adverse effect of head winds on speed of travel over the return leg. These data strongly suggest that by reducing time spent on the water, birds were able to buffer trip durations against adverse effects of strong winds encountered during both commuting and active foraging. Birds also commuted at greater heights with increasing tail wind speed and at lower heights with increasing head wind speed, potentially providing an additional behavioural buffer against the adverse effects of strong head winds during foraging trips. There was no discernible effect of rain on foraging, but the behavioural flexibility recorded here is likely to be critical to maintaining nest attendance patterns and food provisioning rates of chicks across variable environmental conditions encountered at sea.

Top ten tech cars 2019: Self-driving and electric technologies are infiltrating everyday cars—slowly

LIKE A BORED CHILD on a long car trip, an advanced-vehicle enthusiast can be forgiven for asking, Are we there yet? The rollout and adoption of cars that use alternative energy or that drive themselves has been maddeningly slow. IEEE Spectrum's Top 10 Tech Cars has also been posing and pondering that question every year. • Alternative-energy cars, at least in the United States, face head winds in the form of cheap gasoline and the Trump administration's efforts to loosen fuel-economy standards and other climate-change-related regulations. On the self-driving front, it's become painfully clear that the hype has far outrun the reality. • Even so, electric cars really are trickling down to mainstream buyers and budgets. A fine example is the Hyundai Kona Electric crossover, which was a clear choice for our Top 10. And self-driving technology itself really is infiltrating almost every new car on the road, sometimes in ways that aren't immediately apparent to owners: If your new car is equipped with adaptive cruise control, automated emergency braking, or a lane-keeping system, it is locking onto a path toward full autonomy. It's just not as far down that path as some have suggested we'd be by now. This year, though, an important milestone comes in the form of a BMW 3-Series car that can take all the guesswork out of tricky reverse maneuvers. But now, eyes front for this year's Top 10.

The role of weather conditions on running performance in the Boston Marathon from 1972 to 2018.

This study examined the relationship of weather conditions, together with sex and country of origin, with running performance in the Boston Marathon from 1972 to 2018. A total of 580,990 observations from 382,209 different finishers were analyzed using Generalized Additive Mixed Models. Different groups and subgroups were considered such as all runners, near elite 101:200 finishers, near elite 21:100, annual top ten finishers and annual winners. Weather conditions, over the hours of the event, were average air temperature (°C), total precipitations (mm), wet-bulb globe temperature (WBGT) (°C), wind speed (km/h), wind direction (head wind, side wind, tail wind) and barometric pressure (hPa). These effects were examined in a multi-variable model, together with: sex, country of origin, calendar year, an interaction term country:sex and a spline smooth term in function of calendar year and sex. The average temperature, when increasing by 1°C, was related to worsened performance (by 00:01:47 h:min:sec for all finishers and by 00:00:20 h:min:sec for annual winners). Also, the pressure and wet-bulb globe temperature, when increasing, were related to worsened performances. Tail wind improved performances of all groups. Increasing precipitation was significantly (p<0.05) related to worsened performances in all groups except annual winners. Increasing wind speed was also related to worsened performances in all finishers and near elite groups. Kenyans and Ethiopians were the fastest nationalities. The sex differences (men faster than women in all groups) were the largest in near elite groups. Our findings contributed to the knowledge of the performance in Boston Marathon across calendar years, considering as main effects weather conditions, country of origin and sex.

The frost wave hypothesis: How the environment drives autumn departure of migratory waterfowl

Migration phenology plays a critical role in shaping bird life histories. While the spring migration phenology of birds has been widely studied, our understanding about the mechanisms underlying autumn migration is limited. Frost is an indicator of cold weather, food scarcity, and water unavailability, but how frost drives the autumn departure of migratory birds has not yet been quantified. In this study we propose the ‘frost wave hypothesis’, which posits that the autumn departure of waterfowl is driven by a successive wave of the onset of frost. Using bird satellite tracking data and generalized linear mixed models, we analyze how the departure probability of two waterfowl species during autumn migration is affected by frost, accumulated temperature, food, snow, ice, short-term weather conditions (i.e., wind, temperature and precipitation), remaining migration distances, relative stopover duration, and flight distances between stopover sites. We find that bird autumn departure probability sharply increases after the first frost spell when the accumulated temperature reaches 0 °C, facilitated by surface meridional wind and longer remaining migration distances. We underline the dominant effect of frost on autumn departure, as birds tend to leave even under head wind if the time lag since the onset of frost is large. Time constraints that trigger southward departure are likely to be stronger when migrating birds are still far from their wintering site. By riding the frost wave, birds manage to maximize stopover site utilization while escaping harsh environmental conditions. Our findings improve the understanding of annual avian migration and help quantify the impact of global climate change on migratory waterfowl.

Are Pebble Pile Planetesimals Doomed?

In parabolic flight experiments we studied the wind induced erosion of granular beds composed of spherical glass beads at low gravity and low ambient pressure. Varying g-levels were set by centrifugal forces. Expanding existing parameter sets to a pressure range between $p=300-1200\,$Pa and to g-levels of $g=1.1-2.2\,\rm m\,s^{-2}$ erosion thresholds are still consistent with the existing model for wind erosion on planetary surfaces by Shao & Lu (2000). These parameters were the lowest values that could technically be reached by the experiment. The experiments decrease the necessary range of extrapolation of erosion thresholds from verified to currently still unknown values at the conditions of planetesimals in protoplanetary discs. We apply our results to the stability of planetesimals. In inner regions of protoplanetary discs, pebble pile planetesimals below a certain size are not stable but will be disassembled by a head wind.

Analysis on formula principles for “head wind” disease based on apriori and clustering algorithm

Analysis on formula principles for “head wind” disease based on apriori and clustering algorithm