46 research outputs found
The Role Of Microstructure Refinement On The Impact Ignition And Combustion Behavior Of Mechanically Activated Ni/Al Reactive Composites
Metal-based reactive composites have great potential as energetic materials due to their high energy densities and potential uses as structural energetic materials and enhanced blast materials however these materials can be difficult to ignite with typical particle size ranges. Recent work has shown that mechanical activation of reactive powders increases their ignition sensitivity, yet it is not fully understood how the role of microstructure refinement due to the duration of mechanical activation will influence the impact ignition and combustion behavior of these materials. In this work, impact ignition and combustion behavior of compacted mechanically activated Ni/Al reactive powder were studied using a modified Asay shear impact experiment where properties such as the impact ignition threshold, ignition delay time, and combustion velocity were identified as a function of milling time. It was found that the mechanical impact ignition threshold decreases from an impact energy of greater than 500 J to an impact energy of 50 J as the dry milling time increases. The largest jump in sensitivity was between the dry milling times of 25% of critical reaction milling time (tcr) (4.25 min) and 50% tcr (8.5 min) corresponding to the time at which nanolaminate structures begin to form during the mechanical activation process. Differential scanning calorimetry analysis indicates that this jump in the sensitivity to thermal and mechanical impact is dictated by the formation of nanolaminate structures, which reduce the temperature needed to begin the dissolution of nickel into aluminum. It was shown that a milling time of 50%â75% tcr may be near optimal when taking into account both the increased ignition sensitivity of mechanical activated Ni/Al and potential loss in reaction energy for longer milling times. Ignition delays due to the formation of hotspots ranged from 1.2 to 6.5 ms and were observed to be in the same range for all milling times considered less than tcr. Combustion velocities ranged from 20â23 cm/s for thermally ignited samples and from 25â31 cm/s for impacted samples at an impact energy of 200â250 J
Thermal And Mechanical Response Of PBX 9501 Under Contact Excitation
The thermal and mechanical responses of a cyclotetramethylene-tetranitramine-based explosive (PBX 9501) and two non-energetic mock materials (900-21 and PBS 9501) under high-frequency mechanical excitation are presented. Direct contact ultrasound transducers were used to excite samples through a frequency range of 50 kHz to 40 MHz. The mechanical response of each sample was approximated from a contact receiving transducer and trends were confirmed via laser Doppler vibrometry. The steady-state thermal response of the samples was measured at discrete excitation frequencies via infrared thermography. A maximum temperature rise of approximately 15 K was observed in PBX 9501, and the mock materials exhibited similar thermal characteristics. Temperature gradients were calculated to estimate the total heat generated within the samples due to the mechanical excitation. The active heating mechanisms were found to be highly dependent on the frequency of excitation. Possible mechanisms of heating at frequencies below 1 MHz are likely related to bulk motion. Above this frequency, the active heating mechanisms are likely related to particle-scale processes. The observed phenomena may prove useful in the aid of current trace vapor detection methods for explosives
Violation of Boltzmann Equipartition Theorem in Angular Phonon Phase Space Slows down Nanoscale Heat Transfer in Ultrathin Heterofilms
Heat transfer through heterointerfaces is intrinsically hampered by a thermal boundary resistance originating from the discontinuity of the elastic properties. Here, we show that with shrinking dimensions the heat flow from an ultrathin epitaxial film through atomically flat interfaces into a single crystalline substrate is significantly reduced due to violation of Boltzmann equipartition theorem in the angular phonon phase space. For films thinner than the phonons mean free path, we find phonons trapped in the film by total internal reflection, thus suppressing heat transfer. Repopulation of those phonon states, which can escape the film through the interface by transmission and refraction, becomes the bottleneck for cooling. The resulting nonequipartition in the angular phonon phase space slows down the cooling by more than a factor of 2 compared to films governed by phonons diffuse scattering. These allow tailoring of the thermal interface conductance via manipulation of the interface
The ambivalence of losing weight after bariatric surgery
This study is grounded in a phenomenological lifeworld perspective. It aims at providing rich descriptions of lived experience of the process of losing weight after obesity surgery. Two women participated in in-depth interviews four times each during the first postoperative year. Based on the women's experiences, a meaning structureâthe ambivalence of losing weight after obesity surgeryâwas identified across the women's processes of change. This consisted of five core themes: movement and activityâfreedom but new demands and old restraints; eating habits and digestionâthe complexity of change; appearanceâsmaller, but looser; social relationsâstability and change; and being oneselfâvulnerability and self-assurance. These core themes changed over time in terms of dominance. The experience of ambivalence is discussed according to a phenomenological perspective of the body as lived experience
Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond
2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically examined, including electronics and optoelectonics, electrocatalysis and photocatalysis, energy storage, lubrication, plasmonics, solar cells, and photonics. This review focuses on understanding the interplay between ALD precursors and deposition conditions, the resulting film characteristics such as thickness, crystallinity, and morphology, and ultimately device performance. Through rational choice of precursors and conditions, ALD is observed to exhibit potential to meet the varying requirements of widely different applications. Beyond the current state of ALD TMDCs, the future prospects, opportunities, and challenges in different applications are discussed. The authors hope that the review aids in bringing together experts in the fields of ALD, TMDCs, and various applications to eventually realize industrial applications of ALD TMDCs.Peer reviewe
Evidence and/or Experience-Based Knowledge in Lifestyle Treatment of Patients Diagnosed as Obese?
How does washing without water perform compared to the traditional bed bath: a systematic review
Wat is de invloed van het volume van achtergrondmuziek op de emoties, het denken en het gedrag van supermarktmedewerkers?
Contains fulltext :
68960.pdf (publisher's version ) (Open Access)De invloed van verscheidene facetten van achtergrondmuziek op klanten van een
winkel of uitgaansgelegenheid is in het verleden dikwijls onderzocht. Klanten
zijn echter niet de enige aanwezigen in deze omgevingen. Medewerkers maken
doorgaans ook deel uit van de omgeving en het effect van achtergrondmuziek op
deze groep is niet of nauwelijks onderzocht. In dit artikel wordt het effect van een
onderdeel van achtergrondmuziek, namelijk volume, op supermarktmedewerkers
nader onderzocht. Door middel van een experiment onder medewerkers van twee
supermarkten worden een aantal hypothesen, geformuleerd op basis van eerder
onderzoek met name met betrekking tot klanten, over het effect van het volume
van achtergrondmuziek op supermarktmedewerkers getoetst. In dit onderzoek
wordt onder volume verstaan het volume zoals ervaren door de medewerkers van
de supermarkten. Het blijkt dat het volume van achtergrondmuziek van invloed
is op de emoties (= affect) van medewerkers en dan met name op de mate van
opgewektheid. Er bestaat een positieve relatie tussen volume en affect die echter
afgezwakt wordt naarmate de gemoedstoestand van een medewerker voor aanvang
van het werk positiever is. Denken (= cognitie) en affect blijken daarnaast positief
van invloed te zijn op de prestaties van de medewerker en de mate van sociaal contact
onder medewerkers. De resultaten van dit onderzoek kunnen van waarde zijn voor
managers van een supermarkt, maar ook vergelijkbare omgevingen. Er is echter
nog steeds een gebrek aan onderzoek naar andere omgevingsgebonden of muzikale
componenten, hetgeen kansen biedt voor toekomstig onderzoek