Uniformity Of Depth Research Articles

Selective Gate Recessing of GaAs/AIGaAs/lnGaAs Pseudomorphic HEMT Structures Using BCl3 Plasmas

ABSTRACTWet chemical gate recessing of GaAs based devices suffers from poor control and uniformity of the recess etch depth. Electrical variability can be particularly severe for heterojunction devices that contain thin highly doped layers. This problem can be addressed by the use of etch stop layers and the appropriate etch chemistry. In this paper, results on the selective plasma etching of GaAs from InGaAs and AIGaAs etch stop layers are presented. Using a BCl3 plasma, GaAs layers were removed from thin lnxGa(1-X)As (0.12<x<0.25) layers with selectivities >1000 to 1 due to the poor volatility of indium chlorides. With the addition of SFe, the etch process becomes selective to AlxGa (1-X)As due to the formation of a non-volatile AlFX layer. By the judicious choice of etch conditions (high pressure and low power resulting in low DC bias and optimal BCl3/SF6 ratio), isotropie etch profiles with minimal substrate damage and GaAs to Al0.25Ga0.75As selectivities >1000 to 1 have been achieved. Using these etch conditions, pseudomorphic HEMT wafers were selectively plasma gate recessed yielding saturated current uniformities across a 3 inch wafer of <±1.0mA/100μm of gate periphery. Device characteristics and uniformities that are dependent upon the material structure and epitaxial layer thickness and dopant uniformities rather than upon the gate recess process are realized.

Effective irrigation uniformity as related to root zone depth

In models used for relating the yield to irrigation uniformity it has been assumed that the spatial distribution of irrigation water, as measured at the soil surface, is indeed the water distribution at any depth throughout the root zone. In the present paper the distribution of infiltrated water within the soil bulk, as determined by an analytic solution of the two-dimensional unsaturated flow equation, did not conform to this assumption. A new alternative definition of irrigation uniformity is proposed under the assumption that water uptake by roots does not affect the flux distribution within the soil profile. In this analysis the spatial distribution of irrigation water flux at the soil surface, which is the upper boundary condition of the flow equation, is assumed to be a sine function. The solution to this problem indicates that there is a “damping” effect, which increases with soil depth, on the surface flux fluctuations. Furthermore, the actual irrigation uniformity at a given depth below the soil surface depends upon the initial uniformity at the surface and the distance between adjacent water sources. The closer the water sources are to each other, the shallower is the depth needed to damp the oscillations down to a certain level. This may explain why the actual uniformity of drip irrigation is high while the detailed distribution is very nonuniform and on the other hand, why the actual uniformity of sprinkler guns is low while the detailed actual distribution is close to uniform. Two uniformity coefficients are derived in this study: 1. A depth dependent coefficient which is made up of the damping factor that multiplies the flux fluctuations at the soil surface; 2. An effective uniformity coefficient, which is an average of the depth dependent coefficient over a part or the entire root zone. Different degrees of uniformity are expected when water is applied by different irrigation systems having similar uniformity coefficients at the soil surface, but dissimilar distances between the emitters. Assuming that crop yield depends to some extent on the uniformity of water depth actually available to the roots, the yields associated with such irrigation systems will probably also vary.

Hydraulic Downpressure System Performance for Conservation Planting Machines

ABSTRACT AN experimental hydraulic downpressure system was designed and tested on a no-tillage grain drill. Regulated downpressure to individual row units provided centralized downpressure adjustment and unit flotation for improved uniformity of planting depth. The system performed adequately in several years of field use. Passage of the drill over simulated soil undulations produced hydraulic pressure surges which were significantly affected by transmittal distance, field speed, and system pressure. An air damping system reduced the magnitude of the pressure surges for more uniform planting depth. The system could be used to convert existing planters and drills for use in no-tillage conditions.

Development of a High-Efficiency Finishing Process Using ‘Liquid-Bonded Wheel’

In order to improve the removal rate of high precision finishing, a machining process using a new lapping wheel named “Liquid-Bonded Wheel” has been developed. All abrasive grains in this wheel are tightly fastened to each other by the surface tension and the cohesion of bonding liquid. Therefore, the wheel can be manufactured in a short period of process time due to the elimination of the firing process and has a more elastic bond strength than PVA wheel which is known as the softest wheel. This mechanical characteristic provides the process with a decrease of the removal unit and an uniformity of grain depth of cut. The important property of this new process is the ability to finish brittle materials such as silicon monocrystal requiring high accuracy of flatness. This process also has many active grains, resulting in a high removal rate in spite of extremely high degrees of surface finish. Moreover, the weakness of bond strength yields a self-dressing motion of the wheel, and the wheel wear rate may be adjusted by the amount of liquid sprayed. The function can maintain a high removal rate over a long period of process time. Easy truing of the wheel caused by the weakness of bond strength enables the finishing of the arbitrary surface.

Soil Reacting Forces for Disks from Field Measurements

ABSTRACT FOR single-acting, tandem and offset disk harrows, the disk angle can often be adjusted as much as 10 to 25 deg whereas the usual range is 30 to 40 deg for the one-way disk harrow. A field experiment was conducted with a single disk and a multicomponent sensor using a split-plot factorial design, with two tilling sites in the main plots and the disk angle, depth and speed in the subplots. The results indicate that a small disk angle should be used unless it is necessary to improve pentration, reduce skewing or both for the one-way disk harrow; to improve penetration, increase the uniformity of tilling depth or both for the tandem or offset disk harrow. For either implement the minimum depth should be used which is consistent with adequate culti-vation. The draft of the one-way disk harrow and the draft per unit width of cut is such that the former is maximum at 35 deg whereas the latter is maximum at 45 deg. The location of the resultant of the soil reacting forces indi-cates that a soil body affected the geometry of the tool.

CRITERIA OF BELLY BACON DESIRABILITY. II. VISUAL APPRAISAL AND PHYSICAL MEASUREMENTS OF THE BELLY

Variation in the physical dimensions (width and depth) of bacon rashers observed in a population of 730 pigs was more precisely explained by the carcass measurements of backfat and weight than by specific measurements made on the rasher. Ratios among these measurements, including uniformity of rasher depth, could not be predicted from either rasher or carcass measurements. Total fat content and fat–lean distribution through the rasher were associated with measures of carcass or belly fatness but not with carcass weight or with width, depth or uniformity of rasher. Subjective grades applied in this study were primarily a function of fat content, but estimates provided by visual assessment of each rasher were no better correlated with most rasher measurements and fat–lean ratios than carcass backfat or backfat plus specific gravity of the belly. The importance of fat content as a criterion of bacon quality, coupled with the apparent dependence of rasher dimensions and fat–lean distribution on degree of fatness, led to the conclusion that measures of fat made on the carcass or the belly should constitute the primary basis for assessing overall product desirability.

CYCLONIC MICROSEISMS GENERATED IN THE WESTERN NORTH ATLANTIC OCEAN

Nearly all the microseism storms generated by extra-tropical cyclones in the western North Atlantic during the fall and winter seasons of 1948–49 and 1949–50 have been studied, together with some storms that occurred during the 1950–51 fall-winter. Seismograms from a number of east-coast stations and Bermuda were examined for each storm. Each of the microseism storms has been correlated with a particular marine atmospheric disturbance. The period of the microseisms appears to be a function of the depth of water in the generating area, and the regularity of the microseisms appears to be a function of the uniformity of depth in the generating area. Consequently, the position and nature of marine disturbances often can be estimated from the nature of the recorded microseisms. All the evidence on origin tends to negate ocean swell, standing waves produced by interference of ocean swell, and surf as mechanisms producing the observed microseisms. The study suggests atmospheric pulsations, resulting from turbulence or instability, to be at the root of microseism origin. Anomalies of propagation of hurricane microseims suggest the existence of a zone or surface of discontinuity along at least a portion of the outer margin of the east-coast continental shelf.

VI.—The Use of a Geological Datum

A proper interpretation of some geological phenomena requires that allowance shall be made for differential earth-movements that have taken place since the period of occurrence of the events or conditions under consideration.Present differences of level in rocks of the same age may be partly due to actual differences in depth of the sea-floor on which they were deposited, but they may also be the results of subsequent differential earth-movements either of a regional or of a local character, the latter including ‘fauhs.’In order to estimate the amount of displacement or differential movement, it is necessary to select a particular rock as a datum. The rock selected should combine, as far as possible, the following characteristics:—1. It should be comparatively thin.2. It should have a considerable horizontal extension.3. It should combine similarity in physical characters and palæontological contents over a large area, so that uniformity of depth of deposit may be postulated.

The principles of training rivers through tidal estuaries, as illustrated by investigations into the methods of improving the navigation channels of the estuary of the seine

The conditions affecting the training of rivers in the non-tidal portions of their course by jetties, or rubble embankments designated as training walls, are well understood. Training walls substitute a straightened uniform channel for irregularities and varying widths, improving the flow of the current and rendering it uniform, so that scour occurs in the shallow, narrowed portions, and more uniformity of depth is attained.