Movable Portion Research Articles

Economic Design and Construction of Anechoic Chambers

For the past 16 years, the design of anechoic chambers has been the subject of a good deal of acoustic research. Prior research has yielded a design employing a large number of light-density wedges (2.S lb/ft3) which had to be supported a fixed distance from the chamber wall. The design considerations which formed the nucleus of a research program by the Industrial Acoustics Company, Inc., were the following: (1) The wedge had to be made of a rigid material. (2) The over-all length of any anechoic wedge must be maintained as short as physically possible. (3) The wall area covered by a single wedge should be made as large as possible. The first series of investigations made was to determine whether or not the conventional air space could be eliminated. Two figures showing test results of two particular experiments indicate that, if the wedge sizes were maintained constant, there is no advantage in having the air space behind them. It was also observed that the low-frequency absorption could be matched to the high-frequency absorption by altering the wedge-shaped portion, or tapered length, of the anechoic wedge as well as the base depth. In order to maintain as small as physically possible the over-all length of our anechoic-chamber wedges, experiments were performed to show that the standard 4-in.-thick IAC Noise-Lock panel could be used as part of the wedge's length without affecting the acoustic property, in any manner, of either clement. A graph is presented showing the final design curve of the IAC wedge for use in obtaining the length of the anechoic wedge required for any given cutoff frequency, as well as actual test results of wedges constructed to check the IAC design curve. The test method used in the laboratory was to analyze a standing wave pattern produced by a sound source emitting a pure tone. The schematic drawings given show a typical wedge arrangement in the test duct. The method of test used to evaluate a completed installation is slightly different. It is accomplished by generating a pure tone at one point in the room, moving the microphone away from the sound source until the entire room dimension is traversed, and then by comparing the results with those predicted by the inverse-square law. The correlation between IAC laboratory tests and field installations shows excellent agreement, within ±1-db measurement accuracy. The elimination of the air space behind the wedge allows a more efficient use of wedge material. This advantage, plus the use of a more rigid glass-fiber material than previously used, enables a more pleasing appearance to be maintained in the anechoic chamber, as well as a less elaborate construction for movable portions of an IAC anechoic chamber (such as the wedge door or window-wedge plugs). All these features are important to the economic design and over-all performance of an anechoic chamber. The incorporation of a larger base area and a shorter wedge length, coupled with the use of prefabricated structures in which the additional design criteria of quiet intake and exhaust of ventilation air can be provided, as well as the support of the entire structure on suitable vibration eliminators, is strongly recommended. In order to show that a more economical structure can now be manufactured than heretofore possible, a comparison is made of prefabricated and concrete rooms utilizing a new or old wedge design.

A method for the design of holding electromagnets

IN DESIGNING cylindrical holding electromagnets, which consist of a ferromagnetic core, with stationary and movable portions, interlinking a coil of wire, it is desirable to proceed from the specified mechanical and electrical characteristics directly to the physical dimensions of the magnet without the use of trial-and-error methods.

A method for the design of holding electromagnets

The problem discussed is the optimum design of cylindrical holding electromagnets consisting of a ferromagnetic core, with stationary and movable portions, interlinking a coil of wire. These electromagnets are required to hold a switch or contact assembly in a given position as long as power is applied and to release it when power is removed. The electromagnet is not required to pull in the contact assembly; this is done by other means. It is desirable for the design method to proceed from the specified mechanical and electrical characteristics directly to the physical dimensions of the magnet without the use of trial-and-error methods.

Month in the Patent Office

A rolling control system for a jet‐propelled aircraft consists of a pair of vanes 5 mounted diametrically opposite each other in the annular jet exhaust pipe 3 and rotatable in opposite directions by a motor 12 acting through gearing 10, 11 to give a spiral motion to the exhaust gases and thus set up a reaction rolling moment on the aircraft, thereby avoiding loss of control at low speeds. In their normal position the vanes act as flow straighteners for the turbine exhaust. As shown each vane extends across the full width of the exhaust pipe 3, but other constructions are described in which (a) it extends only across part of the pipe width; (b) the vane consists of a central movable portion mounted between fixed end portions; (c) the leading edge portion of the vane is fixed, the trailing edge being movable; (d) the whole vane is fixed, deflection of the exhaust being obtained by spoilers; (e) the vane is fixed, exhaust deflection being obtained by discharging pressure gas through apertures in the surface of the vane.

Month in the Patent Office

In an aircraft with folding wings, the movable portions 5 are connected to the fixed portions 4 by hinges whose axes X—X1 arc inclined and located in the longitudinal plane of the main spars 6, 8 of the wings. In the form shown, the hinge axes converge down‐wardly, the wing portion in front of each hinge being of stepped shape DEFG in plan, while the upper surface of the fixed wing portion 4 to the rear of the hinge is formed with a recess 9 to allow the passage of the lower edge 10 of the rear portion of the movable wing portion 5 during folding and unfolding. The undersurface of the fixed portion is formed with a horizontal extension 11 for supporting the wing portion 5, while the latter carries a flap 12 covering the recess 9 when the wing is extended. The wings may be operated by hydraulic or electric jack; 14, and remotely controlled locking devices 17, 18 may be employed for securing the wings in their extended position.

Obstructive lesions of the descending colon and rectum.

Since all lesions of the descending colon and rectum may become obstructive, they are of interest not only to the proctologist but to the general surgeon, to the internist and sometimes to the urologist and gynecologist. The term rectosigmoid has been discarded, because of variations of interpretations of its boundaries. The movable portion above the pelvic peritoneal reflection is designated as sigmoid, and the fixed portion below as the rectum, which in this discussion will also include the anus. The signs and symptoms of obstructive lesions usually have a mild onset and a gradual increase in severity. As the lesion becomes more and more constricted, the vague abdominal uneasiness progresses to definite discomfort and, later, pain. In some instances the pain may be more intense in the right lower quadrant of the abdomen. Definite changes in bowel movements become more pronounced, until there are real colicky pains and palpable or

Month in the Patent Office

In rudders and like control surfaces consisting of a fixed forward and a movable rear portion there is placed in the open chamber at the rear of the fixed portion a hinged member dividing the chamber into two compartments and to this is secured a pivoted auxiliary surface on the rear member. A rudder composed of fixed part 1 and an after movable part 2, has a division wall 4 in the part 1 which provides a compartment behind it open to the external fluid. To the member 2 is secured an auxiliary surface 3 which is secured by a hinge 6 to a division plate 5 passing through the wall 4 and supported on suitable guides there. For purpose of maintaining the front part of the member 1 fluid tight there is provided a sealing strip 8. In an alternative construction the member 5 is pivotally mounted on the after wall of the division plate 4 and the two surfaces 3, 5 are connected hingedly by an intermediate plate. In a modification of this construction the intermediate plate is dispensed with and the two parts are connected by a pin‐and‐slot mechanism.

SIGMOIDOSCOPY VERSUS X-RAYS IN THE DIAGNOSIS OF TERMINAL BOWEL DISEASE

During the period of thirty-five years since Professor Roentgen discovered the x-rays and Howard Kelly introduced standard rectoscopes, refinements in the technic of roentgenology and improvements in proctoscopes havemade these two agents prime factors in the diagnosis of gastro-intestinal diseases. Each method has its indications, advantages and limitations, and frequently the two are mutually helpful in reaching a correct diagnosis. The roentgen ray has a wide range of applicability and has proved its value in the diagnosis of gastrointestinal lesions, notably in the movable portions of the tract, as the stomach and colon; in demonstrating position, contour, function, points of stasis and defects indicating pathologic changes. In the relatively fixed rectum and distal sigmoid colon, however, which are situated largely within the bony pelvic girdle, the x-rays are of comparatively limited value. Prominent defects are that: An important lesion may be missed entirely. Although the site and apparent extent of

XV.—Experiments and Observations on Crustacea: Part IV. Some Structural Features Pertaining to Glyptonotus

SUMMARY1. Advantage has been taken of the large size of Glyptonotus to study certain structural features, especially skeletal, which cannot be so readily investigated in smaller isopods. Where possible, an attempt has been made to correlate structural peculiarities with functional use.2. The Legs.—The peculiar articulation, analogous to a spheroidal bony joint, between the coxopodites and basipodites of the thoracic limbs, is described in detail. A comparison is instituted between the full flexion-complex of the isopodan and of the brachyuran walking limb. The peræopods are contrasted with the gnathopods of Glyptonotus, and functional peculiarities pertaining to each group of limbs are discussed.3. The Peræon.—The medial split in the thoracic sternites is interpreted as a device for allowing of distension of the body, say, after a meal. The arched thoracic somites articulate with each other in a special way, not by a crossed articulation, like that in a pair of scissors, but by a rocker articulation, like that in a spring clothes-pin; this combination of arch and rocker articulation is interpreted as a means of preventing change of internal volume in body flexion. The phenomena pertaining to the moulting process throw light upon the numerical grouping of the successive fusions of coxæ with somites which have occurred in isopods.4. The Pleon.—The pleon consists of four movable portions, the last four of the seven constituent pieces being welded together. Of the four fused segments, only the first has a complete sternite, like those of somites 1, 2, and 3. In the skeleton of the pleonic floor a wide opening is thus left posteriorly, which is closed by a diaphragm of soft cuticle; part of this diaphragm is elevated into two long parallel folds or valves, one on each side of the anus.5. The Pleonic Appendages.—The protopodite of each of the anterior three pleopods is composed of two complete pieces; a third piece more proximally situated is interpreted, not as evidence of an additional primitive segment, but as a secondary development in the articular membrane. The uropods have acquired their present position by a forward rotation of the sternite of the sixth primitive somite, and the gill-directed surface of the uropod corresponds to the posterior surface of the pleopods. It follows that what has commonly been called the exopodite of the uropod is a real exopodite. In addition to the pleopods, the internal walls of the whole uropodal chamber subserve a respiratory function.6. The Cephalosome.—Two thoracic somites are fused with the head to form a cephalosome. By welded inturnings of the anterior border of these two and of the posterior border of the mandibular cephalic somite a strong internal bracing is formed. The tergites of the maxillary somites have apparently disappeared from the dorsal aspect of the cephalon; the endo-skeletal structures described by Lloyd in Bathynomus, and by him named “sternal alæ,” functionally correspond to these tergites in so far as they serve for attachment of muscles for the maxillæ. These “sternal alæ” (which also appear to form a covering for the maxillary excretory gland) with other ventral endoskeletal structures are described in detail. All are rigidly fixed to the maxillo-sternal framework, which is capable of independent movement.7. The Alimentary Canal.—The foregut of Glyptonotus is not a gastric mill; the muscle-provided involutions of its wall (exactly analogous to those in Bathynomus) are concerned simply with onward propulsion of the food, i.e. with swallowing. Between the midgut and the hindgut, the two opposed ends of which are not in exact alignment, is a strongly contractile part of the gut, which acts as a sphincter. The hepatic cæca could not be examined. Glyptonotus is carnivorous.8. The Eyes and the Chromatophore-System.—By experiment on colour change of Idotea it has been shown that the eye of this animal acts as a double mechanism, the ventral half being functionally separable from the dorsal. Glyptonotus has retractile chromatophores, and probably undergoes colour change in accordance with différent modes of eye illumination. Its eye is divided into two entirely separate parts, one lying on the dorsal the other on the ventral aspect of the cephalon.The cost of providing the illustrations which accompany this paper was defrayed by a grant from the Earl of Moray Endowment for the promotion of research in the University of Edinburgh; and the expense of preparing the blocks was defrayed by a grant from the Carnegie Trust.I have to record my thanks to Dr W. S. Bruce, not only for the material provided, but for information relating to the quarters inhabited by Glyptonotus.

The action of anæsthetics on living tissues. Part II.—The frog's skin

The currents given by the frog’s skin and their variations after excitation both directly and through the nerves have already been studied by many authors, but, as far as I can determine, no one has up to the present time observed the action of anæsthetics on the resting current, and as these phenomena form a fitting sequel to those occurring in nerve (Part I of this series), they form the subject of this paper. It is to be observed that from the nature of the object one of the possible alternative hypotheses in the case of nerve is here excluded, and it is therefore now legitimate to take a further step in explanation of the action of chloroform on the tissues generally. Experiments . Series I . A chamber was constructed of vulcanite, through the bottom of which three non-polarisable electrodes projected. A movable partition of model­ ling wax, luted with moist china-clay, divided one electrode, A, from the other two, C and B (fig. 1). The skin was placed with the outer surface resting on A and C, the movable upper portion of the partition adjusted, and contact effected with the electrode B through a bundle of linen threads soaked in m /10 NaCl solution. In this series the electrode C served merely as a support, and the potential differences between A and B were alone considered.

The British Association: Section A—Mathematical and Physical Science

New Electric Balances, by Sir William Thomson, F.R.S.—These balances are founded On the mutual forces, discovered by Ampère, between the fixed and movable portions of an electric circuit. The mutually-influencing portions are usually circular rings. Circular coils or rings are fixed, with their planes horizontal, to the ends of the beam of a balance, and are each acted on by two horizontal fixed rings placed one above and the other below the movable ring. Six grades of instrument are made, named centi-ampere, deci-ampere, ampere, deca-ampere, hecto-ampere, and kilo-ampere balance. The range of each balance is about 25. Thus, the centi-ampere balance will measure currents of from 2 to 50 centi-amperes, while the kilo-ampere balance will measure currents of from 100 to 2500 amperes. Since the indications of the instrument depend on the mutual forces between two parts of an electric circuit of permanent form and relative position, they are not subject to the changes with time which are so troublesome in instruments the constants of which depend on the strength of permanent magnets.