Barbara Schmitz

Heat of Adsorption for Hydrogen in Microporous High‐Surface‐Area Materials

The limited resources of fossil fuels will soon require a change to renewable energies. The ideal energy carrier for mobile applications is hydrogen, but the problem of an adequate and safe storage system is still unsolved. One of the possibilities for hydrogen storage is physisorption in porous materials. The big advantage of molecular hydrogen storage is that short refuelling times can be realized due to the extremely fast kinetics. Additionally, no extra heat management is needed as the heat of adsorption is lower than for other storage processes, for example in metal hydrides. On the other hand, owing to this low heat of adsorption, a cryosystem is needed to reach high storage capacities. Microporous materials possessing a high specific surface area (SSA), for example carbon nanotubes, activated carbon, zeolites, and coordination polymers or metal–organic frameworks (MOFs), show a high hydrogen uptake at low temperatures, typically 77 K. Characteristic for this cryo-adsorption in porous materials is that the maximum hydrogen uptake at high pressures depends linearly on the SSA of the material. At low pressures distinct differences in the hydrogen uptake exist for the different materials. Therefore, the pressure to reach, for example, 80% of the maximum storage capacity, differs strongly between the materials. For all materials the hydrogen uptake decreases with increasing temperature. The strength of this decrease as well as the hydrogen uptake at low pressures are governed by the heat of adsorption. Typically, the isosteric heat of adsorption is calculated from the adsorption isotherms measured at 77 K and 87 K since these temperatures can easily be realized by liquid nitrogen and liquid argon, respectively. This small temperature range leads to a very high uncertainty in the heat of adsorption. Only in a few publications is the isosteric heat of adsorption determined with higher accuracy from several isotherms measured at various temperatures. Herein, we present hydrogen adsorption isotherms measured over a wide temperature (77–298 K) and pressure ACHTUNGTRENNUNG(0–20 bar) range. This allows the determination of the heat of adsorption for a wide range of surface coverage with very high accuracy. For the first time different microporous materials have been investigated systematically and their heats of adsorption are correlated to the structures of the materials. Two activated carbon samples, Norit R0.8 and Takeda 4A, with BET SSAs of 1384 mg 1 and 397 mg 1 respectively, and four different metal–organic frameworks, MOF-5, Cu-BTC, MIL-53 and MIL-101, with SSAs between 902 mg 1 and 3293 mg 1 have been investigated. The hydrogen uptake was measured with an automated Sieverts’ apparatus (PCTPro2000, HyEnergy, USA). Figure 1 shows the dependence of the hydrogen uptake on the pressure as an example for Cu-BTC (for other materials, see the Supporting Information). For all materials the isotherms at

Morphological and physiological changes in central auditory neurons following unilateral foreleg amputation in larval crickets

Summary1.In view of the surprising recent demonstration that developmentally one-eared female crickets can track sound sources (Huber et al. 1984), we have looked for correlates in the morphological and physiological properties of auditory interneurons of these animals. One foreleg was amputated in the 3rd/4th or penultimate (8/9th) larval instar; in both cases the leg regenerated without developing a functional ear. In the adult stage, these animals were studied first for their phonotactic behavior and then by intracellular recording and staining; three types of auditory interneurons in the prothoracic ganglion were identified: the omega neuron ON1, and the ascending neurons AN1 and AN2.2.Of these three neuron types, those that normally receive excitatory input from the side now deafferented send dendrites across the midline of the ganglion, along specific pathways, to end in the auditory neuropil of the intact side (Figs. 1–4).3.The new connections are functional, as shown by the responses of the neurons to synthesized calling songs presented to the remaining ear. With respect to the copying of chirp structure, threshold curves and intensity characteristics, these neurons respond like cells in intact animals that are presented with the same stimulus on the side ipsilateral to the main input region of the neurons (Figs. 2–4). The implication is that in animals with one ear missing, functional pathways within the central nervous system are reorganized, resulting in better orientation of one-eared animals.

Influence of [Mo6Br8F6](2-) Cluster Unit Inclusion within the Mesoporous Solid MIL-101 on Hydrogen Storage Performance

The inclusion of (TBA)(2)Mo(6)Br(8)F(6) (TBA = tetrabutylammonium) containing [Mo(6)Br(8)F(6)](2-) cluster units within the pores of the mesoporous chromium carboxylate MIL-101 (MIL stand for Materials from Institut Lavoisier) has been studied. X-ray powder diffraction, thermal analysis, elemental analysis, solid-state NMR, and infrared spectroscopy have evidenced the successful loading of the cluster. In a second step, the hydrogen sorption properties of the model cluster loaded metal organic framework (MOF) system have been analyzed and compared to those of the pure MOF sample, through a combination of adsorption isotherms (77 K, room temperature), thermal desorption spectroscopy, and calorimetry (calculated and experimental) in order to evaluate the hydrogen storage efficiency of the cluster loading.

Biophysics of directional hearing in the frog Eleutherodactylus coqui

Summary1.We used laser vibrometry and free field sound stimulation to study the frequency responses of the eardrum and the lateral body wall of awake male Eleutherodactylus coqui.2.The eardrum snowed one of two distinct frequency responses depending on whether the glottis was open (GO response) or closed (GC response) during the measurement.3.The lateral body wall vibrated with a maximum amplitude close to that of the eardrum and in the same frequency range.4.Covering the frogs body wall with vaseline reduced the vibration amplitude of the GC response by up to 15 dB.5.When a closed sound delivery system was used to stimulate a local area of the body wall the eardrum also showed one of two types of responses.6.These results suggest that sound is transmitted via the lung cavity to the internal surface of the eardrum. This lung input has a significant influence on the vibrations of the eardrum even when the glottis is closed.7.The vibration amplitude of the eardrum changed with the angle of sound incidence. The directionality was most pronounced in a narrow frequency range between the two main frequencies of the conspecific advertisement call.

Neuroplasticity and phonotaxis in monaural adult female crickets (Gryllus bimaculatus de Geer)

SummaryOne foreleg was amputated at mid-femur in adultGryllus bimaculatus females. In phonotaxis tests these monaural crickets show course deviations and circling towards the intact side (Fig. 1). Mean course stability is best at 60 and 70 dB (Fig. 2). Here it differs significantly from a threshold value for orientated walking in females operated on the day of adult moult, but not in those operated two weeks later. The orientational performance improves with the interval between amputation and test (Fig. 3).Centripetal cobalt backfills reveal degeneration of tympanal nerve fibers on the amputated side (Fig. 4B, C). The mean number of intact afferents crossing the midline of the prothoracic ganglion is increased in monaural versus binaural crickets. Maximum transmidline extension is not correlated with the period of deafferentation (Fig. 5).Intracellular recording and staining of prothoracic auditory interneurons shows some axonal sprouts in ON1i (intact side) and ON2, but no significant physiological changes (Figs. 6A, D; 8A, C, E, G). Apart from axonal sprouts ON1a (amputated side) may show a few dendritic sprouts into the intact auditory neuropil (Figs. 6C, 7). Excitation in some ON1a-cells reveals functional contacts to intact auditory afferents (via crossing dendrites or possibly crossing afferents, Figs. 6e, 7, 8F). Morphological and associated physiological changes start early in AN2a (amputated side). The degree of crossing dendrites and contralateral excitation increases with postoperative age (Figs. 8H, 9).

Phonotaxis inGryllus campestris L. (Orthoptera, Gryllidae)

SummaryPhonotaxis of receptive female field crickets (Gryllus campestris L.) towards a taped model of the species-specific calling song (Fig. 1) presented azimuthally at 12 different sound pressure levels, ranging from 39 to 106.5 dB, is investigated using a locomotion compensator. The orientational performance of the crickets is analysed in the intact state (1.), as well as after occlusion of both prothoracic spiracles (2.), both posterior tympana (3.), both prothoracic spiracles and both posterior tympana (4.), one posterior tympanum and one prothoracic spiracle at a time (5.).1.In intact female crickets acoustic orientation on average starts at 44 dB. The orientational performance improves steadily up to 79.5 dB, deteriorates slightly at 86 and 91.5 dB and remarkably at 106.5 dB calling song intensity (Figs. 3, 4 and 11).2.Following wax occlusion of both prothoracic spiracles (Figs. 5 and 6) behavioural threshold of phonotaxis is raised by on average 5 dB to 49 dB. The course of the intensity curve is similar to that evaluated for intact crickets, the orientational performance at a given intensity being merely slightly reduced (Fig. 11).3.Occlusion of both posterior tympana (Figs. 7 and 8) does not abolish the capability of acoustic orientation. Compared to intact animals the behavioural threshold is only raised by on average 17.5 dB to 61.5 dB (Fig. 11). Orientational performance at suprathreshold intensities improves with increasing song intensity, but remains inferior to that of intact crickets unless a 106.5 dB calling song is presented.4.Phonotaxis is even evident after occlusion of the posterior tympana and the prothoracic spiracles with wax (Figs. 9 and 10). This operation results in an effective attenuation of on average 30 dB, the behavioural threshold being raised to 74 dB (Fig. 11). At suprathreshold intensities orientational performance is further reduced compared to that of crickets after occlusion of the posterior tympana only.5.Occlusion of a posterior tympanum and a prothoracic spiracle on opposite sides results in a stable course deviation of on average 49 ° towards the side of the intact posterior tympanum at 61.5 to 91.5 dB (Figs. 13, 14A and B). This demonstrates that the effect of an occluded posterior tympanum overrides that of an occluded prothoracic spiracle. Occlusion of these sound entrances on the same side results in strong turning tendencies towards the intact side, which increase with calling song intensity (Fig. 14C and D). Except in a single crickets run performed at 106.5 dB, stable courses are no longer found (Fig. 15). Thus, phonotaxis is more strongly impaired than after occlusion of these sound entrances on opposite sides.

A High Heat of Adsorption for Hydrogen in Magnesium Formate

The hydrogen adsorption and desorption properties of a microporous metal-organic framework, magnesium formate, are investigated. The material has channel-like pores of approximately 3.4 A diameter. The pore size is below the kinetic diameter of nitrogen and causes a breakdown of the linear relationship between maximum hydrogen uptake and specific surface area measured by nitrogen adsorption. From the experimental isotherms the isosteric heat of adsorption for hydrogen is calculated with very high accuracy over a wide range of surface coverage, up to 80 %. The isosteric heat of adsorption is 6.5-7 kJ mol(-1) which is one of the highest values ever observed over the whole range of surface coverage.

Acoustic orientation in adult, female crickets (Gryllus bimaculatus de Geer) after unilateral foreleg amputation in the larva

SummaryInGryllus bimaculatus females one foreleg was amputated at the coxa-trochanter joint in the 2nd, 4th or 8th/9th larval instar. A leg of up to normal length is regenerated (Fig. 1) but it lacks a functional ear. In spite of the, usually shorter, regenerated foreleg, the adult one-eared crickets show no impairments in walking when tested on a locomotion compensator. Without sound they walk erratically and most of them weakly circle towards the intact side (Fig. 2).With calling song presentation three response types can be distinguished:tracking (Fig. 3A), ‘hanging on’ (Fig. 3B) or continuouscircling towards the intact side (Fig. 3C, D). Turning tendencies in monaurals increase with song intensity and exceed those of intact and bilaterally operated animals (Fig. 4). Course deviations towards the intact side also slightly increase with intensity (Fig. 5). Course stability is reduced compared to that of intact animals but exceeds that of bilaterally operated crickets (Figs. 5, 6). It is best at 60 dB and deteriorates at higher sound intensities (Fig. 6). The percentage of monaurals tracking or ‘hanging on’ decreases with increasing intensity (Fig. 7B). Tracking is established in most animals but it is limited to a narrow intensity range (Fig. 7A, C). Apart from an increased percentage of tracking after early operations (Fig. 7D), there are no prominent changes in orientational parameters with the date of foreleg amputation.Reamputation of the regenerated leg in the adult monaurals does not significantly impair acoustic orientation (Figs. 8, 9), but occlusion of the ipsilateral prothoracic spiracle does (Figs. 10, 11).An attempt is made to correlate the behavioral performance with the activity of auditory interneurons which have undergone morphological and physiological changes (Fig. 12).

Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

SummaryDirectionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed.Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3).In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2–4 and 5A). Directions differing by 30°–60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40–200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40–250 mm/s, Fig. 5A).In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B).The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.