Effects of non-local exchange on core level shifts for gas-phase and adsorbed molecules

Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional

Catalysis in flow: Operando study of Pd catalyst speciation and leaching

A custom-made plug flow reactor was designed and constructed to examine the behaviour of Pd catalysts during Suzuki-Miyaura cross-coupling reactions. Spatial-temporal resolution of catalyst activation, deactivation and leaching processes can be obtained by single-pass experiments. Subsequent deployment of the flow reactor in a XAS beam line revealed speciation of Pd along the catalyst bed

Significant quantum effects in hydrogen activation

Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ∼190 K and for D2 up to ∼140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation

An inset fed square microstrip patch antenna to improve the return loss characteristics for 5G applications

32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017 --19 August 2017 through 26 August 2017 -- --132402In this study, a square microstrip patch antenna operating in millimeter wave frequencies with improved return loss characteristics is proposed. The proposed patch antenna operates at 30 GHz which is among the projected 5G communication frequencies and has a novel geometry with diamond-shaped slots. The first design in this work is a conventional inset fed square microstrip patch antenna. It has a quarter wavelength impedance matching line. The dimensions are determined according to the usual design considerations. Low return loss and high bandwidth requirements motivates us to modify the antenna design. Therefore, we add diamond - shaped slots on the patch which leads to an additional increase in the system bandwidth as much as 46 MHz and a reduction in the return loss level up to 10.751 dB. Due to these novel characteristics, the proposed patch antenna design is conjectured to be a suitable candidate to address the requirements of 5G communication systems. The operating frequency of the proposed antenna can be tuned by changing the geometrical dimensions from microwave to the THz region. © 2017 URSI

An Inset Fed Square Microstrip Patch Antenna to Improve the Return Loss Characteristics for 5G Applications

32nd General Assembly and Scientific Symposium of the International-Union-of-Radio-Science (URSI GASS) -- AUG 19-26, 2017 -- Montreal, CANADAWOS: 000463723600036In this study, a square microstrip patch antenna operating in millimeter wave frequencies with improved return loss characteristics is proposed. The proposed patch antenna operates at 30 GHz which is among the projected 5G communication frequencies and has a novel geometry with diamond-shaped slots. The first design in this work is a conventional inset fed square microstrip patch antenna. It has a quarter wavelength impedance matching line. The dimensions are determined according to the usual design considerations. Low return loss and high bandwidth requirements motivates us to modify the antenna design. Therefore, we add diamond -shaped slots on the patch which leads to an additional increase in the system bandwidth as much as 46 MHz and a reduction in the return loss level up to 10.751 dB. Due to these novel characteristics, the proposed patch antenna design is conjectured to be a suitable candidate to address the requirements of 5G communication systems. The operating frequency of the proposed antenna can be tuned by changing the geometrical dimensions from microwave to the THz region.Int Union Radio Sc

Investigation of the Effects of the Slot Parameters on a Patch Antenna at 28 GHz Related to the Operating Wavelength

In this paper, we introduce the effects of the slots etched on a square patch antenna on the radiation characteristics related to the operating wavelength at 28 GHz. We first design an inset fed patch antenna with a square geometry operating at 28 GHz. Then we etch a rhombic shaped slot in the middle point of the patch and perform a parametric analysis for the edge dimensions of 1/10, 1/100 and 1/1000 of the wavelength. Additionally, we move the slot along the vertical axis with the distances from the center of 1/10, 1/100 and 1/1000 of the wavelength and analyze the effects. Finally, after etching additional slots on the bottom edges of the antenna and shift them in +y direction we acquire extra bandwidth and lower return loss levels. With this final design, we reach at an increase for the bandwidth of 180 MHz and a reduction of 25.51 dB for reflection coefficient level. These novel features yield the proposed structure a suitable model for 5G communications and it can clearly be concluded that there is a strong relationship between the antenna characteristics and slot parameters related to the operating wavelength

Influence of Soldiers on Exploratory Foraging Behavior in the Formosan Subterranean Termite, Coptotermes formosanus (Blattodea: Rhinotermitidae)

Termites are eusocial insects that live in organized colonies consisting of reproductives, workers, and soldiers. Soldiers are specialized for defense but are expensive to maintain, as they are incapable of husbandry and must be fed and groomed by workers. The soldiers of several species influence foraging behavior by acting as scouts that initiate foraging or by mediating worker behavioral plasticity during food exploration. These behaviors imply that soldiers may play a keystone role in termite colony function, apart from defense. Subterranean termite workers tunnel through soil in search of food while accompanied by varying proportions of soldiers, depending on the species and colony conditions. Previous studies have shown that soldiers accelerate worker exploratory tunneling behavior in two Reticulitermes species, the colonies of which contain fewer than 2% soldiers. This effect, however, is unknown in other subterranean species with different soldier proportions. In this study, we examined the influence of soldiers on exploratory foraging behavior in the Formosan subterranean termite, Coptotermes formosanus Shiraki, which is an economically devastating invasive species that maintains a relatively high soldier proportion (about 10%). When 100 foraging workers were grouped with 0, 2, 10, or 30 soldiers in two-dimensional foraging arenas, we found no significant effect of soldiers on the tunnel length, branch pattern, food source interception, or food collected within 96 h. These results suggest that C. formosanus colonies maintain food exploration efficiency regardless of soldier proportion variation.</jats:p