Vibration and comfort I. Translational seat vibration

A series of studies of discomfort caused by multi-axis vibration at the seat, feet and back of seated persons is described. This first paper reports on studies with translational seat vibration. Two experiments concerned with the effects of level, frequency and direction of the translational vibration of a firm flat seat are reported.

At octave centre frequencies from 1 to 63 Hz the first experiment determined the levels of fore-and-aft, lateral and vertical seat vibration which caused discomfort equivalent to 0.5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8m/s²r.m.s. 10 Hz vertical seat vibration and subject transmissibilities were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 100 Hz. In both studies the feet of subjects were not vibrated and there was no backrest.

It was concluded that the shapes of equivalent comfort contours need not normally depend on vibration level. The forms of both individual and group equivalent comfort contours and seat-to-head transmissibilities are presented. Significant correlations were found between subject characteristics (size and transmissibility) and subject relative discomfort. The males and females produced similar equivalent comfort contours.

Information on the computerized application of the method of constant stimuli which was developed for the series of experiments is presented together with a consideration of alternative methods of determining the central tendency of the data. A method of assessing the effect of vibrator distortion on judgements of equivalent discomfort is also defined.     

Vibration and comfort HI. Translational vibration of the feet and back

The effects on discomfort of the frequency and direction of the translational vibration of a footrest and flat firm backrest have been studied in two experiments. At frequencies in the range 2.5-63 Hz, the first experiment determined the levels of fore-and-aft, lateral and vertical vibration of the feet of seated subjects which caused them discomfort equivalent to that from 0.8 m/s² r.m.s. 10 Hz vertical vibration of a firm flat seat. The levels of fore-and-aft, lateral and vertical vibration at the back of a seat which were equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined in the second experiment. The vibration of the feet or back occurred without simultaneous vibration at the seat.

Individual and group equivalent comfort contours are presented. It is concluded that the data provide a useful initial indication of the relative contribution of foot and back vibration to discomfort. Equivalent comfort contours for foot vibration were similar for all three directions of vibration. The contours for vibration of the back show a high sensitivity to fore-and-aft vibration. The results obtained from two additional studies show that vibration from a backrest and other variations in seating conditions can influence subject comfort.     

Whole-body vibration and visual performance: an examination of spatial filtering and time-dependency

Two experiments have examined the effects of whole-body vibration on visual performance. The first experiment concerned alphanumeric reading performance and contrast thresholds for gratings subtending 7-5, 10 and 12-5 cycles per degree (c deg)^?1. Seated subjects were exposed to vertical sinusoidal whole-body vibration (4 Hz, 2-5 ms^?2 r.m.s.). Greatest reading errors occurred with characters exhibiting a high spatial complexity in their vertical axis. Reductions in contrast sensitivity due to vibration increased with increasing spatial frequency, the greatest loss occurring with horizontally orientated gratings.

In the second experiment, contrast thresholds for horizontally orientated gratings subtending 1-5 and 12-5cdeg^?1 were obtained from ten subjects at five-minute intervals during a 60-minute whole-body vibration exposure (20 Hz I -7 m s ^?2 r.m.s.), a 20-minute pre-exposure and a 60-minute post-exposure period. There were no significant changes in contrast thresholds for gratings subtending 1-5cdeg^minus;1 during or after vibration exposure. A large variation was found in the effect of vibration upon performance with the higher spatial frequency grating both during and after vibration exposure. Significant correlations between vertical head motion and contrast sensitivity were obtained with five of the ten subjects, suggesting that time-dependent changes in seat-to-head transmissibility were partly responsible for the results. Other time-dependent changes were found with the high spatial frequency grating. Possible explanations are discussed.     

Bedside safety rails: assessment of strength requirements and the appropriateness of current designs

This second paper in a series of studies of the discomfort produced by multi-axis vibration is concerned with rotational seat vibration. The effects of level, frequency and direction of the roll, pitch and yaw vibration of a firm flat seat have been studied in two experiments. At octave centre frequencies in the range 1-31.5 Hz the first experiment determined the levels of roll, pitch and yaw seat vibration which caused discomfort equivalent to 0-5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 31.5 Hz. In all cases the axis of rotation passed through the centre of the seat surface. There was no vibration of the feet and no backrest.

It was concluded that the shape of equivalent comfort contours need not normally depend on vibration, level. Both individual and group equivalent comfort contours are presented. Although there were significant correlations between subject size and subject relative discomfort it is not thought that these correlations have much practical application. In all three axes the median contours of vibration acceleration increase in proportion to vibration frequency. Sensitivity is greatest for roll vibration and least for yaw vibration of the seat.     

A comparison of the wind magnitudes obtained from the microwave radiometer onboard IRS‐P4 satellite and the ERS‐2 scatterometer

Wind speeds obtained from the Multifrequency Scanning Microwave Radiometer (MSMR) are evaluated with those obtained from the European Remote Sensing Satellite (ERS‐2) scatterometer over the global oceans over the period 15 June 1999 to 23 August 1999. A detailed statistical analysis has been carried out to assess the accuracy of the MSMR wind magnitudes. The analysis consists of an examination of the mean bias and Root Mean Square (rms) differences between the two gridded fields for different regions. The biases and the rms errors are different for different regions, being less over the tropical oceans and more over the polar regions. The biases range from about 3?m?s^?1 in the tropics to over 6?m?s^?1 in high latitudes, with the global average of 4.2?m?s^?1. These biases are different for different wind speed ranges, being highest for the low wind speed range (0–4?m?s^?1). The global standard deviation (SD) is found to be 2.2?m?s^?1. The MSMR overestimated wind magnitude.     

Inter-comparison of wind profiles in the tropical boundary layer remotely sensed from GPS radiosonde and Doppler wind lidar

Winds play a very important role in the dynamics of the lower atmosphere, and there is a need to obtain vertical distribution of winds at high spatio-temporal resolution for various observational and modelling applications. Profiles of wind speed and direction obtained at two tropical Indian stations using a Doppler wind lidar during the Indian southwest monsoon season were inter-compared with those obtained simultaneously from GPS upper-air sounding (radiosonde). Mean wind speeds at Mahbubnagar (16.73° N, 77.98° E, 445 m above mean sea level) compare well in magnitude for the entire height range from 100 m to 2000 m. The mean difference in wind speed between the two techniques ranged from ?0.81 m s^?1 to +0.41 m s^?1, and the standard deviation of wind speed differences ranged between 1.03 m s^?1 and 1.95 m s^?1. Wind direction by both techniques compared well up to about 1200 m height and then deviated slightly from each other at heights above, with a standard deviation in difference of 19°–48°. At Pune (18^○32′ N, 73^○51′ E, 559 m above mean sea level), wind speed by both techniques matched well throughout the altitude range, but with a constant difference of about 1 m s^?1. The root mean square deviation in wind speed ranged from 1.0 to 1.6 m s^?1 and that in wind direction from 20° to 45°. The bias and spread in both wind speed and direction for the two stations were computed and are discussed. The study shows that the inter-comparison of wind profiles obtained by the two independent techniques is very good under conditions of low wind speeds, and they show larger deviation when wind speeds are large, probably due the drift of the radiosonde balloon away from the location.     

Enhancement of vertical cloud-induced radiative heating in East Asian monsoon circulation derived from CloudSat-CALIPSO observations

ABSTRACT

Improving the understanding of cloud–radiation–monsoon interactions is difficult due to the limited knowledge regarding the impacts of vertical cloud radiative forcing on monsoon circulation. Here, we focus on the annual cycle of the vertical structure of cloud-induced radiative heating (CRH) to evaluate further their impacts on the East Asian monsoon circulation (100°–140° E, 20°–45° N) derived from satellite observations and reanalysis datasets. Entire troposphere and lower stratosphere are heated by vertical CRH, with the peak reaching 1 K day^?1 at the mid-level troposphere (4–10 km) during summer. Although radiative warming occurs below 3 km from the prevailing stratocumulus, widespread weak radiative cooling (approximately ?0.2 K day^?1) occurs at a wide vertical range above 3 km during winter. Consequently, the wind vector variations resulting from vertical CRH highly coincide with the monsoon circulation, leading to the increase in wind speeds by 1.8 and 0.5 m s^?1 during summer and winter, respectively, while a weakly negative influence (about 0.3 m s^?1) occurs at the low-level troposphere below 3 km during winter. Although high clouds, stratiform clouds, and stratocumulus dominate these wind vector variations, deep convective clouds generate the strongest updraft (up to 7 m s^?1) amongst all cloud categories despite their low occurrence frequency. Results highlight the important enhancement of vertical CRH to East Asian monsoon circulation by perturbing the vertical structure of heating rate.     

Variations of surface boundary layer parameters associated with Cyclone Gonu over the Arabian Sea using QuikSCAT data

This study attempted to quantify the variations of the surface marine atmospheric boundary layer (MABL) parameters associated with the tropical Cyclone Gonu formed over the Arabian Sea during 30 May–7 June 2007 (just after the monsoon onset). These characteristics were evaluated in terms of surface wind, drag coefficient, wind stress, horizontal divergence, and frictional velocity using 0.5° × 0.5° resolution Quick Scatterometer (QuikSCAT) wind products. The variation of these different surface boundary layer parameters was studied for three defined cyclone life stages: prior to the formation, during, and after the cyclone passage. Drastic variations of the MABL parameters during the passage of the cyclone were observed. The wind strength increased from 12 to 22 m s^?1 in association with different stages of Gonu. Frictional velocity increased from a value of 0.1–0.6 m s^?1 during the formative stage of the system to a high value of 0.3–1.4 m s^?1 during the mature stage. Drag coefficient varied from 1.5 × 10^?3 to 2.5 × 10^?3 during the occurrence of Gonu. Wind stress values varied from 0.4 to 1.1 N m^?2. Wind stress curl values varied from 10 × 10^?7 to 45 × 10^?7 N m^?3. Generally, convergent winds prevailed with the numerical value of divergence varying from 0 to –4 × 10^?5 s^?1. Maximum variations of the wind parameters were found in the wall cloud region of the cyclone. The parameters returned to normally observed values in 1–3 days after the cyclone passage.     

Equivalent comfort contours for fore-and-aft,lateral, and vertical whole-body vibration in the frequency range 1.0 to 10 Hz

Abstract

Standards assume vibration discomfort depends on the frequency and direction of whole-body vibration, with the same weightings for frequency and direction at all magnitudes. This study determined equivalent comfort contours from 1.0 to 10?Hz in each of three directions (fore-and-aft, lateral, vertical) at magnitudes in the range 0.1 to 3.5?ms^?2?r.m.s. Twenty-four subjects sat on a rigid flat seat with and without a beanbag, altering the pressure distribution on the seat but not the transmission of vibration. The rate of growth of vibration discomfort with increasing magnitude of vibration differed between the directions of vibration and varied with the frequency of vibration. The frequency-dependence and direction-dependence of discomfort, therefore, depended on the magnitude of vibration. The beanbag did not affect the frequency-dependence or direction-dependence of vibration discomfort. It is concluded that different weightings for the frequency and direction of vibration are required for low and high magnitude vibration.

Practitioner summary: When evaluating whole-body vibration to predict vibration discomfort, the weightings appropriate to different frequencies and different directions of vibration should depend on the magnitude of vibration. This is overlooked in all current methods of evaluating the severity of whole-body vibration.     

An algorithm for the retrieval of sea surface wind fields using X-band TerraSAR-X data

TerraSAR-X (TS-X) is a new, fully polarized X-band synthetic aperture radar (SAR) satellite, which is a successor of the Spaceborne Imaging Radar X-band Synthetic Aperture Radar (SIR-X-SAR) and the SRTM. TS-X has provided high-quality image products over land and oceans for scientific and commercial users since its launch in June 2007. In this article, a new geophysical model function (GMF) is presented to retrieve sea surface wind speeds at a height of 10 m (U ₁₀) based on TS-X data obtained with VV polarization in the ScanSAR, StripMap and Spotlight modes. The X-band GMF was validated by comparing the retrieved wind speeds from the TS-X data with in situ observations, the high-resolution limited area model (HIRLAM) and QuikSCAT scatterometer measurements. The bias and root mean square (RMS) values were 0.03 and 2.33 m s^?1, respectively, when compared with the co-located wind measurements derived from QuikSCAT. To apply the newly developed GMF to the TS-X data obtained in HH polarization, we analysed the C-band SAR polarization models and extended them to the X-band SAR data. The sea surface wind speeds were retrieved using the X-band GMF from pairs of TS-X images obtained in dual-polarization mode (i.e. VV and HH). The retrieved results were also validated by comparing with QuikSCAT measurements and the results of the German Weather Service (DWD) atmospheric model. The obtained RMS was 2.50 m s^?1 when compared with the co-located wind measurements derived from the QuikSCAT, and the absolute error was 2.24 m s^?1 when compared with DWD results.     

The effect of posture and vibration magnitude on the vertical vibration transmissibility of tractor suspension system

The efficiency of suspension seat can be influenced by several factors such as the input vibration, the dynamic characteristics of the seat and the dynamic characteristics of the human body. The objective of this paper is to study the effect of sitting postures and vibration magnitude on the vibration transmissibility of a suspension system of an agricultural tractor seat. Eleven (11) healthy male subjects participated in the study. All subjects were asked to sit on the suspension system. Four (4) different sitting postures were investigated – i) “relax”, ii) “slouch”, iii) “tense”, and iv) “with backrest support”. All subjects were exposed to random vertical vibration in the range of 1–20 Hz, at three vibration magnitudes - 0.5, 1.0 and 2.0 m/s² r.m.s for 60 s. The results showed that there were three pronounced peaks in the seat transmissibility, with the primary resonance was found at 1.75–2.5 Hz for every sitting postures. The “backrest” condition had the highest transmissibility resonance (1.46), while the “slouch” posture had the highest Seat Effective Amplitude Transmissibility (SEAT) values (64.7%). Changes in vibration magnitude for “relax” posture from 0.5 to 2.0 m/s² r.m.s resulted in greater reduction in the primary resonance frequency of seat transmissibility. The SEAT values decreased with increased vibration magnitude. It can be suggested that variations in posture and vibration magnitude affected the vibration transmission through the suspension system, indicating the non-linear effect on the interaction between the human body and the suspension system.Relevance to industry: Investigating the posture adopted during agricultural activities, and the effects of various magnitudes of vibration on the suspension system's performance are beneficial to the industry. The findings regarding their influence on the human body may be used to optimize the suspension system's performance.     

An improved look-up table technique for geophysical parameters from SSM/I

An improved look-up table technique is developed to calculate meteorological parameters from Special Sensor Microwave/Imager (SSM/I) measurements. The method, which is based on a look-up table and an extrapolation and interpolation technique used in the weather prediction model, gives results comparable to or better than the regression method for the total precipitable water (TPW), surface wind speed (V), and cloud liquid water path (LWP). Applied to a noise-free data set (dependent test) TPW, V and LWP are retrieved with a rms. accuracy of 0.26 kg m^-2, 0.28 m s^-1 and 0.002 kg m^-2, respectively. If the random noise of the SSM/I radiometer is taken into account in the retrieval, the r.m.s. increases to 0.84 kg m^-2, 1.08 m s^-1 and 0.013 kg m^-2, respectively. The method is applied to a set of over 520 SSM/I measurements from the DMSP-F8 satellite for which collocated radiosondes launched from ships are available. The rms. (bias) of TPW and V was 2.91 (-0.61) kg m^-2 and 2.75 (-0.13) m s^-1, respectively. We use the improved look-up table technique to calculate the monthly mean global distribution of surface wind for August 1989 and compare the results with the Comprehensive Ocean-Atmosphere Data Set (COADS) for the same month. The rms. error and mean differences for the monthly mean values of sea surface wind speed between the retrievals and COADS data are 1.01 m s^-1 and 0.03 m s^-1, respectively. We also calculate LWP for October 1987 and compare it with the LWP derived from cloud optical thicknesses of International Satellite Cloud Climatology Project (ISCCP) dataset. Good agreement is obtained. The extension of the method to calculate cloud water and water vapour profiles is discussed.     

Generation of 3-D geoidal surface of the Bay of Bengal lithosphere and its tectonic implications

We compare wind speeds derived from analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1986 to 1992 with wind speeds retrieved from three space borne instruments: the Geosat altimeter, the Special Sensor Microwave/Imager (SSM/I) microwave radiometer and the European Remote Sensing (ERS-I) scatterometer. The comparison reveals imperfections in both ECMWF and SSM/I wind speeds.

The ECMWF wind speeds are systematically underestimated with respect to the satellite wind speeds in the tropical Pacific and the Atlantic Ocean before May 1989. After the changes to the ECMWF model in May 1989, the differences vanish in the Atlantic and are reduced by about 50 per cent in the Pacific Ocean. However, the differences between ECMWF and satellite wind speeds are greater than those observed between the satellite wind speeds themselves: yearly differences between the satellite and the ECMWF wind speeds are greater than 2 m s^?1 in tropical regions whereas intercomparison of satellite wind speeds reveals differences within ±1m s ^?1. In September 1991 a new version of the ECMWF model was introduced which greatly altered the wind analyses, both in the tropics and in the southern Pacific Ocean. At the global scale, the mean ECMWF-SSM/I wind difference is close to 0m s^?1 before the September 1991 changes and increases to 0·4m s^?1 following the changes, meaning that the ECMWF wind speeds are 5 per cent less than the SSM/I wind speeds, an observation which may also be made from the ECMWF-ERS 1 comparisons.

The SSM/I wind speeds appear as underestimates with respect to the other three data sets in regions of high and moderate wind speeds, in particular in the high northern latitudes and in the Arabian sea, which could result from a Wentz algorithm directional flaw.     

Review of “Ethnic Variables in Human Factors Engineering. Edited ” by Alphonse ChApanis-(Baltimore: Johns Hopkins University Press, 1975.) [Pp. xviii + 290.] £9-50.

Measurements were made of the motion of a ship, and of the consequent seasickness experienced by passengers. Data are presented for 17 voyages of up to 6?hours duration, involving 4915 passengers. Vertical motion occurred up to 1·0 m s^?2 r.m.s. and vomiting incidence of up to nearly 40% was encountered.

Both vomiting incidence and illness rating correlated well with root mean square vertical z-axis acceleration. The effect of exposure duration was also investigated, producing suggestions for a combined measure of acceleration and time. Multiple regression analysis with all six axes of motion revealed only a small increase in correlation when all directions of motion in addition to the z-axis were taken into account.     

Validation of ERS-2 SAR offshore wind-speed maps in the North Sea

Wind maps are retrieved from ERS-2 Synthetic Aperture Radar (SAR) scenes by the CMOD-IFR2 and CMOD4 algorithms for 61 cases at the Horns Rev site in the North Sea and compared to meteorological in situ observations from a mast located 14?km offshore. The in situ data are corrected for flow distortion and sea-level changes prior to validating the SAR wind maps. The SAR wind maps are area-averaged by a simple footprint method assuming neutral stability and with three nonlinear weighting footprint methods including correction for stability. From a physical point of view, the latter is more correct. However, between in situ and SAR-derived wind-speed estimates comparison results of the nonlinear footprint values are statistically less correlated (R ²=0.73–0.77) and the standard error (SE) is larger (>1.5?m?s^?1) than results from the simple footprint (R ²=0.78–0.80 and SE=1.3?m?s^?1). The results are found with wind direction determined from wind streaks in the SAR images by Fast Fourier Transform. Using in situ wind direction as input to the CMOD-IFR2 and CMOD4 algorithms yields even better linear regression results, e.g. for the simple footprint method R ²=0.88 and SE=0.9?m?s^?1. SAR wind maps may be useful for mapping of future offshore wind resources.     

Response of the seated human body to whole-body vertical vibration: discomfort caused by sinusoidal vibration

Frequency weightings for predicting vibration discomfort assume the same frequency-dependence at all magnitudes of vibration, whereas biodynamic studies show that the frequency-dependence of the human body depends on the magnitude of vibration. This study investigated how the frequency-dependence of vibration discomfort depends on the acceleration and the force at the subject–seat interface. Using magnitude estimation, 20 males and 20 females judged their discomfort caused by sinusoidal vertical acceleration at 13 frequencies (1–16 Hz) at magnitudes from 0.1 to 4.0 ms^? 2 r.m.s. The frequency-dependence of their equivalent comfort contours depended on the magnitude of vibration, but was less dependent on the magnitude of dynamic force than the magnitude of acceleration, consistent with the biodynamic non-linearity of the body causing some of the magnitude-dependence of equivalent comfort contours. There were significant associations between the biodynamic responses and subjective responses at all frequencies in the range 1–16 Hz.

Practitioner Summary: Vertical seat vibration causes discomfort in many forms of transport. This study provides the frequency-dependence of vibration discomfort over a range of vibration magnitudes and shows how the frequency weightings in the current standards can be improved.     

Biodynamic response analysis of semi-supine human under varying vertical excitations

The biodynamic responses of semi-supine humans exposed to varying vertical vibration magnitudes (0.125–1.0 m/s² r.m.s.) are studied employing a multi-body modeling approach. The model comprises five rigid segments: the head, upper torso, lower torso, thigh, and leg. The viscoelastic property of tissues at joints and body-support interface are incorporated using the Kelvin-Voigt model. The dynamic model parameters identified through optimization are employed to capture the transmissibility responses of different body segments at varying vibration magnitudes. The Monte-Carlo simulation is performed to ascertain the effect of uncertainty of the model parameter and body mass on the biodynamic responses at different vibration magnitudes. The calibrated model accurately predicts the decrease in the primary resonance frequency with the increase in vibration magnitude. This nonlinearity is also apparent in vertical transmissibility responses of all the body segments. The effect of uncertainty of model parameters and body mass on the transmissibility responses is prominent near resonance frequency, while their effect on the apparent mass response is consistent across the entire frequency spectrum. The Monte-Carlo simulation illustrates higher dispersion in the transmissibility responses of the head and thorax at 1.0 m/s² r.m.s. compared to at 0.125 m/s² r.m.s. Therefore effective restraint systems are required at the head and thorax to counter the impact of high vibration magnitudes experienced during spaceflight.     

Effects of whole-body vertical shock-type vibration on human ability for fine manual control

The effects of vertical (z-axis) whole-body shock-type vibration on the ability for fine manual control were examined. The amplitudes and frequency of the shocks was varied, but a constant frequency-weighted acceleration of 1·25 m/s² r. m. s. was maintained. The examination of the shock's effects was carried out using an experimental system that simulated the actual workplace of earth-moving machinery. Control was measured using a first-order pursuit tracking-test, in which a seated subject was asked to use both hands to direct a cursor on a monitor using a steering wheel. Although the magnitude of shocks (peak amplitude of 6-10 m/s²) and the number of shocks per unit time (shock cycle of 10-40 s) were varied, and two types of shock (symmetric and asymmetric) used, no shock effect could be found by calculating an integrated square of tracking error during the whole exposure time. The tracking error only increased significantly during the moments that the subjects were exposed to a symmetrically shaped shock that reached the highest peak value (for the experiment) of 10 m/s². The results suggested that shocks with peak amplitudes below defined value induce no evident effect on the steering of vehicles.     

A detection problem: Sensitivity and uncertainty analysis of a land surface temperature approach to detecting dynamics of water use by groundwater-dependent vegetation

Sustainable management of groundwater-dependent vegetation (GDV) requires the accurate identification of GDVs, characterisation of their water use dynamics and an understanding of associated errors. This paper presents sensitivity and uncertainty analyses of one GDV mapping method which uses temperature differences between time-series of modelled and observed land surface temperature (LST) to detect groundwater use by vegetation in a subtropical woodland. Uncertainty in modelled LST was quantified using the Jacobian method with error variances obtained from literature. Groundwater use was inferred where modelled and observed LST were significantly different using a Student's t-test. Modelled LST was most sensitive to low-range wind speeds (<1.5 m s⁻¹), low-range vegetation height (<=0.5 m), and low-range leaf area index (<=0.5 m² m⁻²), limiting the detectability of groundwater use by vegetation under such conditions. The model-data approach was well-suited to detection of GDV because model-data errors were lowest for climatic conditions conducive to groundwater use.     

Bounds on the rate of disjunctive codes

A binary code is said to be a disjunctive (s, ?) cover-free code if it is an incidence matrix of a family of sets where the intersection of any ? sets is not covered by the union of any other s sets of this family. A binary code is said to be a list-decoding disjunctive of strength s with list size L if it is an incidence matrix of a family of sets where the union of any s sets can cover no more that L ? 1 other sets of this family. For L = ? = 1, both definitions coincide, and the corresponding binary code is called a disjunctive s-code. This paper is aimed at improving previously known and obtaining new bounds on the rate of these codes. The most interesting of the new results is a lower bound on the rate of disjunctive (s, ?) cover-free codes obtained by random coding over the ensemble of binary constant-weight codes; its ratio to the best known upper bound converges as s → ∞, with an arbitrary fixed ? ≥ 1, to the limit 2e ^?2 = 0.271 ... In the classical case of ? = 1, this means that the upper bound on the rate of disjunctive s-codes constructed in 1982 by D’yachkov and Rykov is asymptotically attained up to a constant factor a, 2e ^?2 ≤ a ≤ 1.