Mass Aggregation Research Articles

MID-PALEOZOIC TRILOBITE LAGERSTATTEN: MODELS OF DIAGENETICALLY ENHANCED OBRUTION DEPOSITS

Spectacular trilobite Lagerstatten occur in distinctive offshore calcareous mudstone facies through the Late Ordovician to Devonian, and reflect a combination of mass mortality or molting and burial, coupled with early diagenetic enhancement. Evidence indicates two distinct modes of burial, Type I and II assemblages, which show evidence for burial without or with seafloor disturbance, respectively. Type I assemblages suggest rapid (hours to days), but not instantaneous burial, without bottom disruption, enabling preservation of in situ behavior, including mass aggregations and molt ensembles. Most occurrences contain bedding planes in which trilobites exhibit incipient disarticulation. These assemblages were buried by cascades of flocculated sediment from hypopycnal, detached flows. Type II assemblages show well-articulated, enrolled, semi-enrolled, and outstretched trilobites in varied orientations relative to bedding. In such cases, bottom flows and seafloor disruption by storm or seismic disturbances in shallow waters suspended large amounts of flocculated muds as viscous slurries, which developed into hyperpycnal flows that entrained carcasses of trilobites and other organisms. In many cases, both Type I and II obrution was followed by additional sedimentation, geochemical zones moved upward through the sediment column, and there was little tendency to form diagenetic overprints. Alternatively, if burial was followed by an interval of sediment starvation, the sediments were bioturbated and very early diagenetic mineralization was superimposed, first, in rare cases, as mineralized soft parts in entombed carcasses, and later as pyritization of burrow linings. Development of the concretionary layers required more prolonged periods of stability of the sulfate reduction zone. Cementation of sediment shielded organism bodies from most or all effects of compaction. Thus, ironically, the best preservation of delicate remains required rapid burial, associated with mass mortality, and very low rates of background sedimentation following the event.

Small Amphipathic Molecules Modulate Secondary Structure and Amyloid Fibril-forming Kinetics of Alzheimer Disease Peptide Aβ1–42

Amyloid fibril formation is associated with a number of debilitating systemic and neurodegenerative diseases. One of the most prominent is Alzheimer disease in which aggregation and deposition of the Aβ peptide occur. Aβ is widely considered to mediate the extensive neuronal loss observed in this disease through the formation of soluble oligomeric species, with the final fibrillar end product of the aggregation process being relatively inert. Factors that influence the aggregation of these amyloid-forming proteins are therefore very important. We have screened a library of 96 amphipathic molecules for effects on Aβ(1-42) aggregation and self-association. We find, using thioflavin T fluorescence and electron microscopy assays, that 30 of the molecules inhibit the aggregation process, whereas 36 activate fibril formation. Several activators and inhibitors were subjected to further analysis using analytical ultracentrifugation and circular dichroism. Activators typically display a 1:10 peptide:detergent stoichiometry for maximal activation, whereas the inhibitors are effective at a 1:1 stoichiometry. Analytical ultracentrifugation and circular dichroism experiments show that activators promote a mixture of unfolded and β-sheet structures and rapidly form large aggregates, whereas inhibitors induce α-helical structures that form stable dimeric/trimeric oligomers. The results suggest that Aβ(1-42) contains at least one small molecule binding site, which modulates the secondary structure and aggregation processes. Further studies of the binding of these compounds to Aβ may provide insight for developing therapeutic strategies aimed at stabilizing Aβ in a favorable conformation.

Identification of a new phospholipase D in Carica papaya latex

Phospholipase D (PLD) is a lipolytic enzyme involved in signal transduction, vesicle trafficking and membrane metabolism. It catalyzes the hydrolysis and transphosphatidylation of glycerophospholipids at the terminal phosphodiester bond. The presence of a PLD in the latex of Carica papaya (CpPLD1) was demonstrated by transphosphatidylation of phosphatidylcholine (PtdCho) in the presence of 2% ethanol. Although the protein could not be purified to homogeneity due to its presence in high molecular mass aggregates, a protein band was separated by SDS-PAGE after SDS/chloroform–methanol/TCA–acetone extraction of the latex insoluble fraction. This material was digested with trypsin and the amino acid sequences of the tryptic peptides were determined by micro-LC/ESI/MS/MS. These sequences were used to identify a partial cDNA (723bp) from expressed sequence tags (ESTs) of C. papaya. Based upon EST sequences, a full-length gene was identified in the genome of C. papaya, with an open reading frame of 2424bp encoding a protein of 808 amino acid residues, with a theoretical molecular mass of 92.05kDa. From sequence analysis, CpPLD1 was identified as a PLD belonging to the plant phosphatidylcholine phosphatidohydrolase family.

Influence of aggregation on the antioxidative capacity of milk peptides

This study investigated the effects of pH and addition of genistein prior to freeze-drying on the aggregation of reconstituted antioxidative milk peptides. The peptides having molecular masses below 6.5kDa aggregated into higher mass aggregates of 16.9kDa after tryptic hydrolysis for 30min. Subsequent freeze-drying at pH 2.0 further promoted the aggregation of peptides to aggregates of 26.6kDa, both in the absence and presence of genistein. The reconstituted peptides clustered into macroaggregates of 6μm, having oxygen radical absorbance capacity (ORACFL) between 0.07 and 0.22μmol Trolox equivalent (TE)mg−1 protein. Although freeze-drying at pH 6.5 promoted the aggregation of peptides, the reconstituted peptides retained a size of 150–170nm and had an ORACFL of 0.59–0.88μmol TEmg−1 protein. The addition of genistein synergistically increased Trolox equivalent antioxidant capacity, compared with the reconstituted milk peptide alone (P<0.05).

Population balance model for drying of droplets containing aggregating nanoparticles

AbstractDrying of droplets containing nanoscaled particles is investigated for the first drying stage by means of a population balance model. The novelty of the model consists in the consideration of not only gas‐side heat and mass transfer, and liquid‐side diffusion, but also aggregation as a particulate process. Size‐dependency of particle mobility links liquid‐side mass transport and aggregation, leading to different particle concentration profiles in the droplet depending on the thermal conditions and aggregation kinetics. The main focus of this work lies on the influence of the aggregation kinetics on the profiles, the time of crust formation and the resulting droplet porosity at the end of the first drying stage. Model validation and justification is performed by use of experimental data from literature. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Cellular Internalization of Monomeric and Oligomeric Amyloid-Beta 42 Peptide

Amyloid beta (Abeta) is the major component of extracellular plaques found in Alzheimer's disease (AD). Uptake of Abeta from extracellular to intracellular space, which is likely by endocytosis, appears to be an important process for understanding AD pathology (Friedrich et al., PNAS 2010; Hu et al., PNAS 2009). It may also be a promising target for treatment and prevention.We aimed to study biophysical details of Abeta uptake, and to determine the uptake kinetics for different Abeta forms: monomers, oligomers, higher molecular mass aggregates of Abeta in and small fibrils. We used neuroblastoma (Sh-EP) cells as a model for neurons. Uptakes kinetic were followed by using the fluorescent labelled Abeta 42 that was monomerized and was purified by gel filtration. Abeta 42 peptide was added to the cell culture medium and the amount of intracellular aggregates was quantified using automated fluorescence microscopy.We compared uptake kinetics and aggregation kinetics in buffer and in cell culture medium at different Abeta 42 concentrations to test whether aggregation precedes uptake or vice versa. To compare the uptake of different Abeta species, pre-aggregated Abeta oligomers or small fibrils were added to the cells. We found that pre-aggregation accelerated the formation of intracellular aggregates, which suggests that Abeta oligomers and / or small fibrils may be taken up more rapidly than Abeta monomer.In the future the form and location of intracellular Abeta will be monitored by high resolution fluorescence nanoscopy combined with atomic force microscopy.

Analysis of soluble proteins/aggregates derived from gluten-emulsifiers systems

According to their amphiphilic nature, emulsifiers as Sodium Stearoyl Lactylate (SSL) and Diacetyl Tartaric Acid Esters of Monoglycerides (DATEM) favor interactions between dough components, although the mechanisms of action are not fully elucidated. There is quite information about the nature of emulsifier–gluten protein interaction and its consequence in breadmaking quality, but no reports were found about structural changes in gluten proteins produced by SSL and DATEM and their influence in aggregation–disaggregation gluten protein phenomena. For this reason the aim of this work was to investigate changes on gluten protein structure induced by SSL and DATEM; through the analysis of the nature of soluble aggregates by different SDS-PAGE techniques, and gliadins and glutenins extracted from gluten samples by RP-HPLC. At 1% level, SSL allowed the solubilization of a large proportion of high molecular mass aggregates, suggesting that at this high level, this emulsifier cause changes in native gluten protein network. Nevertheless, no significant differences in the protein quantity extracted of the distinct gliadins and glutenins were observed. On the other hand, the emulsifier SSL at 0.5% (w/w) level also allowed the extraction of a high percentage of γ-gliadins and low molecular weight glutenins in comparison with gluten and gluten-DATEM samples. In conclusion distinct quantity and quality of gliadins and glutenins were extracted from gluten samples, depending on the level and the chemical structure of each emulsifier.

A predator–prey model for moon-triggered clumping in Saturn’s rings

UVIS occultation data show clumping in Saturn’s F ring and at the B ring outer edge, indicating aggregation and disaggregation at these locations that are perturbed by Prometheus and by Mimas. The inferred timescales range from hours to months. Occultation profiles of the edge show wide variability, indicating perturbations by local mass aggregations. Structure near the B ring edge is seen in power spectral analysis at scales 200–2000 m. Similar structure is also seen at the strongest density waves, with significance increasing with resonance strength. For the B ring outer edge, the strongest structure is seen at longitudes 90° and 270° relative to Mimas. This indicates a direct relation between the moon and the ring clumping. We propose that the collective behavior of the ring particles resembles a predator–prey system: the mean aggregate size is the prey, which feeds the velocity dispersion; conversely, increasing dispersion breaks up the aggregates. Moons may trigger clumping by streamline crowding, which reduces the relative velocity, leading to more aggregation and more clumping. Disaggregation may follow from disruptive collisions or tidal shedding as the clumps stir the relative velocity. For realistic values of the parameters this yields a limit cycle behavior, as for the ecology of foxes and hares or the “boom-bust” economic cycle. Solving for the long-term behavior of this forced system gives a periodic response at the perturbing frequency, with a phase lag roughly consistent with the UVIS occultation measurements. We conclude that the agitation by the moons in the F ring and at the B ring outer edge drives aggregation and disaggregation in the forcing frame. This agitation of the ring material may also allow fortuitous formation of solid objects from the temporary clumps, via stochastic processes like compaction, adhesion, sintering or reorganization that drives the denser parts of the aggregate to the center or ejects the lighter elements. Any of these more persistent objects would then orbit at the Kepler rate. We would also expect the formation of clumps and some more permanent objects at the other perturbed regions in the rings… including satellite resonances, shepherded ring edges, and near embedded objects like Pan and Daphnis (where the aggregation/disaggregation cycles are forced similar to Prometheus forcing of the F ring).

The Giants Among Us

The patent world is undergoing a change of seismic proportions. A small number of entities have been quietly amassing vast treasuries of patents. These are not the typical patent trolls that we have come to expect. Rather, these entities have investors such Apple, Google, Microsoft, Sony, the World Bank, and non-profit institutions. The largest and most secretive of these has accumulated a staggering 30,000-60,000 patents.Investing thousands of hours of research and using publicly available sources, we have pieced together a detailed picture of these giants and their activities. We consider first the potential positive effects, including facilitating appropriate rewards for forgotten inventors, creating a market to connect innovators with those who can manufacture their inventions, and most important, operating as a form of insurance – something akin to an Anti-Troll defense fund.We turn next to the potential harmful economic effects, including operating as a tax on current production and facilitating horizontal collusion as well as single firm anticompetitive gamesmanship that can raise a rival’s costs. Most important, we note that mass aggregation may not be an activity that society wants to encourage, given that the successful aggregator is likely to be the one that frightens the greatest number of companies in the most terrifying way. We argue that mass aggregators have created a new market for monetization of patents. It is vast, rapidly growing, and largely unregulated. We conclude with some normative recommendations, including that proper monitoring and regulation will require a shift in the definition of markets as well as a different view of corporations and their agents.

The dark matter assembly of the Local Group in constrained cosmological simulations of a Λ cold dark matter universe

We make detailed theoretical predictions for the assembly properties of the Local Group (LG) in the standard LambdaCDM cosmological model. We use three cosmological N-body dark matter simulations from the CLUES project, which are designed to reproduce the main dynamical features of the matter distribution down to the scale of a few Mpc around the LG. Additionally, we use the results of an unconstrained simulation with a sixty times larger volume to calibrate the influence of cosmic variance. We characterize the Mass Aggregation History (MAH) for each halo by three characteristic times, the formation, assembly and last major merger times. A major merger is defined by a minimal mass ratio of 10:1. We find that the three LGs share a similar MAH with formation and last major merger epochs placed on average \approx 10 - 12 Gyr ago. Between 12% and 17% of the halos in the mass range 5 x 10^11 Msol/h < M_h < 5 x 10^12 Msol/h have a similar MAH. In a set of pairs of halos within the same mass range, a fraction of 1% to 3% share similar formation properties as both halos in the simulated LG. An unsolved question posed by our results is the dynamical origin of the MAH of the LGs. The isolation criteria commonly used to define LG-like halos in unconstrained simulations do not narrow down the halo population into a set with quiet MAHs, nor does a further constraint to reside in a low density environment. The quiet MAH of the LGs provides a favorable environment for the formation of disk galaxies like the Milky Way and M31. The timing for the beginning of the last major merger in the Milky Way dark matter halo matches with the gas rich merger origin for the thick component in the galactic disk. Our results support the view that the specific large and mid scale environment around the Local Group play a critical role in shaping its MAH and hence its baryonic structure at present.

Structure of β-lactoglobulin microgels formed during heating as revealed by small-angle X-ray scattering and light scattering

We have investigated the structure of microgels formed during heating of demineralized β-lactoglobulin (βlg) solutions at pH 5.9 by small-angle X-ray scattering (SAXS) and light scattering. First, unheated βlg solutions were characterized at different pH values between 2.0 and 7.0. At pH 5.9, βlg solutions contain mainly dimers (with a radius of approx. 2 nm), which coexist with a small number of larger oligomers (approx. 4 nm). Afterwards, βlg microgels, which form upon heating, were studied. They exhibit an average hydrodynamic radius around 130 ± 20 nm and an average molar mass around 7 × 10 8 g mol −1. We followed the temporal evolution of the various structures that form after different heating times using subsequent SAXS measurements of the entire sample, the soluble fraction where the βlg microgels were removed, and the solvent. After an hour of heating at 85 °C the maximum yield of the βlg microgels (ca. 70%) is almost reached. Interestingly, the SAXS data show a correlation peak corresponding to a characteristic distance of about 9 nm, indicating an internal organization of the microgels. During the heating procedure the pH increases from pH 5.9 to approximately 6.6, which is induced by the partial conversion of βlg into βlg microgels that exhibit less buffering capacity than native protein. The remaining soluble fraction consists of native βlg and some small aggregates, whose number increases on the cost of native βlg as heating time proceeds. We propose that the formation of these lower molecular mass aggregates is triggered by the increased pH.

Spatial displacement of Odonata in south-west Siberia

A brief account is presented of mass dragonfly migrations observed previously in Russia and West Siberia in particular. A mass migration in Libellula quadrimaculata is described in detail. It occurred on 1 July 1981 in the south-western part of the West Siberian Plain in the valley of the Ishym River. From 1968 to 2008 we studied population dynamics, spatial distribution and displacement in dragonflies in the West Siberian forest-steppe. Detailed research was conducted at the biological station of the Russian Academy of Sciences near the Chany Lake. Mass migrations in L. quadrimaculata and some Leucorrhinia spp. followed situations with an extremely high population density and local mass aggregations and occurred with a period of c.10 years, correlated with fluctuation of water level in the region, mainly in the south. It is suggested that dragonfly migration not only optimizes their population size but increases the rate of transport of chemical elements and organic matter to dry land from eutrophic wate...

On a model for mass aggregation with maximal size

We study a kinetic mean-field equation for a system of particles with different sizes, in which particles are allowed to coagulate only if their sizes sum up to a prescribed time-dependent value. We prove well-posedness of this model, study the existence of self-similar solutions, and analyze the large-time behavior mostly by numerical simulations. Depending on the parameter $\Dconst$, which controls the probability of coagulation, we observe two different scenarios: For $\Dconst>2$ there exist two self-similar solutions to the mean field equation, of which one is unstable. In numerical simulations we observe that for all initial data the rescaled solutions converge to the stable self-similar solution. For $\Dconst<2$, however, no self-similar behavior occurs as the solutions converge in the original variables to a limit that depends strongly on the initial data. We prove rigorously a corresponding statement for $\Dconst\in (0,1/3)$. Simulations for the cross-over case $\Dconst=2$ are not completely conclusive, but indicate that, depending on the initial data, part of the mass evolves in a self-similar fashion whereas another part of the mass remains in the small particles.

Interaction between whey proteins and lipids during light-induced oxidation

Dairy products are a suitable group for polyunsaturated fatty acid (PUFA) fortification, but are very susceptible to light-induced oxidation. In this study, the combined effect of light and PUFA fortification on the stability of milk proteins and on the formation of protein-lipid complexes was studied. Therefore, emulsions were prepared containing whey proteins and lipids with a different degree of unsaturation (olive, soybean, fish and algae oil). PUFA stimulated the protein oxidation process, even after complete degradation of the photosensitizer. First order reaction kinetics were established for riboflavin and tryptophan degradation, as well as the formation of N-formylkynurenine, a tryptophan degradation product. Oxidation was further characterised by degradation of the essential amino acids lysine, histidine, methionine and tyrosine. Protein-lipid adduct formation, measured fluorometrically and by the protein-bound carbonyl groups, could be linked with a decreased extractability of the unsaturated lipids from the emulsion, but also caused the formation of protein aggregates of high molecular mass.

Environmental cues or conspecific attraction as causes for egg mass aggregation in hydrobiosid caddisflies

The distribution of egg masses throughout the environment can strongly influence the population dynamics of aquatic insects. Many species lay eggs in aggregations and most eggs will subsequently hatch from only a few locations—knowing how and why these aggregations arise is therefore needed to understand the population dynamics of these species. The hydrobiosid caddisfly Ulmerochorema rubiconum lays eggs in large aggregations on the undersides of emergent rocks in streams. Our aim was to test whether females oviposit in response to conspecific egg masses or the environmental characteristics of rocks by manipulating the number and age of egg masses initially present on rocks and monitoring the accumulation of new masses. Our first experiment used rocks that had recently been used for oviposition and initial egg masses encompassed a range of ages; our second used rocks with no history of oviposition and initial masses of uniform age. Females did not respond to conspecific eggs of any age, as removing initial egg masses had no impact on the number of new masses laid in either experiment. There was a strong positive relationship between the number of initial and new masses, regardless of whether initial egg masses were removed, at the scale of whole rocks and for rock microhabitats. The results suggest that females select oviposition sites based primarily on physical characteristics of emergent rocks. We demonstrate for the first time that the spatial arrangement of egg masses may be consistent and predictable through time, with females showing a high degree of fidelity for particular rocks and microhabitats.

GALAXY DOWNSIZING EVIDENCED BY HYBRID EVOLUTIONARY TRACKS

An unified picture of stellar and halo mass build-up as a function of mass is presented. Inferred stellar-dark halo mass relations of galaxies, Ms-Mh, out to z=4 together with average LCDM halo mass aggregation histories (MAHs) are used for inferring average Ms growth histories, the Galaxian Hybrid Evolutionary Tracks (GHETs). The more massive the galaxy, the earlier transited in average from an active regime of Ms growth to a passive one: log(Mtran/Msun)=10.30+0.55z ("population downsizing"), where Mtran is the typical transition stellar mass. This result agrees with independent observational determinations based on the evolution of the galaxy stellar mass function decomposition into blue and red galaxies. The specific star formation rate, SSFR, predicted from the derivative of the GHET is consistent with direct measures of the SSFR for galaxies at different z's. The average GHETs of galaxies smaller than Mtran at z=0 (Ms~10^10.3 Msun) did not reach the quiescent regime, and for them, the lower the mass, the faster the later Ms growth rate ("downsizing in SSFR"). The GHETs allow to predict the transition rate in number density of active to passive population; the predicted values agree with direct estimates of growth rate in number density for the (massive) red population up to z~1. We show that LCDM-based models of disk galaxy evolution are able to reproduce the low-mass side of the Ms-Mh relation at z~0, but at higher z's disagree strongly with the GHETs: models do not reproduce the downsizing in SSFR and the high SSFR of low mass galaxies. (Abridged)

First report on mass aggregation of opiliones in China

Gregariousness is a widespread behavior among harvestmen, with reports for species from South and North America, Europe and India. The present note reports an enormous aggregation (300,000 individuals) of the harvestman Pseudogagrella sp. (Sclerosomatidae: Gagrellinae) in the tropical rain forest of Xishuangbanna, southern prefecture of Yunnan Province, China. The aggregation was found during winter months, from November to March, in five adjacent, but clearly defined patches ranging from 1 to 6 m2. Females comprised the greater part of the aggregation and only a few males were found in the patches. With the rise in temperature, the density of individuals reduced considerably, and most of them accumulated in a single patch and finally disappeared by the end of April

Diagnosis of pancreatic tuberculosis by combined, contrast-enhanced sonography and endoscopic ultrasound-guided fine-needle aspiration.

A 79-year-old woman complaining of epigastric pain was examined by her local physician, who found an abdominal mass and referred the patient to our department. Abdominal plain computed tomography revealed a mass, 50mm in size, with slight calcification on the ventral side of the head of the pancreas. On abdominal ultrasound, the mass lesion consisted of an aggregation of hypoechoic masses, with a heterogeneous hyperechoic region at its center. On contrast ultrasonography, only the hyperechoic region was stained. (18)F-Fluorodeoxyglucose-positron emission tomography (FDG-PET) revealed FDG accumulation in the same region. It was difficult to differentiate between a malignant pancreatic tumor and an inflammatory disease on imaging, but since QuantiFERON TB2G testing was positive, pancreatic tuberculosis was suspected, and endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNA) was performed to obtain a definitive diagnosis. Samples from the hypoechoic region consisted of necrotic tissue, while those from the hyperechoic region consisted of pancreatic tissue together with granulation tissue. BCG immunostaining was positive, and a diagnosis of pancreatic tuberculosis was made. If EUS-FNA is performed on stained areas seen on contrast ultrasonography, this will probably enable a more accurate diagnosis of pancreatic tuberculosis with low invasiveness.

Effect of alternative processes on the yield and physicochemical characterization of protein concentrates from Amaranthus cruentus

Three different processes for the preparation of amaranth protein concentrates (APCs) were investigated with respect to the yield and physicochemical characteristics. The first was the conventional process for isolating protein (standard process), the second included an acid washing step prior to protein extraction (acid washing process) and the third included heating (50 °C) during the alkaline extraction step (thermal process). The protein yields were 17.8 and 25.6% for the acid washing and thermal processes, respectively. The concentrates were analyzed by SDS-PAGE, free sulfhydryl groups (SH), differential scanning calorimetry (DSC), size-exclusion high performance liquid chromatography (SE-HPLC), solubility in water and in 0.05 mol L −1 NaCl at pH 3.0, 4.5 and 7.0, phenolic compounds content and color parameters. The results indicated that the acid washing process had positive effects on the composition, color parameters, protein solubility and thermal stability of the concentrates. The thermal process also brought about positive effects on the characteristics of the proteins and color parameters although it negatively affected solubility due to the formation of high molar mass aggregates. The conventional process, when compared with the thermal and acid washing processes, adversely affected the properties evaluated.

NUMERICAL MODELING OF THE COAGULATION AND POROSITY EVOLUTION OF DUST AGGREGATES

Porosity evolution of dust aggregates is crucial in understanding dust evolution in protoplanetary disks. In this study, we present useful tools to study the coagulation and porosity evolution of dust aggregates. First, we present a new numerical method for simulating dust coagulation and porosity evolution as an extension of the conventional Smoluchowski equation. This method follows the evolution of the mean porosity for each aggregate mass simultaneously with the evolution of the mass distribution function. This method reproduces the results of previous Monte Carlo simulations with much less computational expense. Second, we propose a new collision model for porous dust aggregates on the basis of our N-body experiments on aggregate collisions. We first obtain empirical data on porosity changes between the classical limits of ballistic cluster-cluster and particle-cluster aggregation. Using the data, we construct a recipe for the porosity change due to general hit-and-stick collisions as well as formulae for the aerodynamical and collisional cross sections. Simple coagulation simulations using the extended Smoluchowski method show that our collision model explains the fractal dimensions of porous aggregates observed in a full N-body simulation and a laboratory experiment. Besides, we discover that aggregates at the high-mass end of the distribution can have a considerably small aerodynamical cross section per unit mass compared with aggregates of lower masses. We point out an important implication of this discovery for dust growth in protoplanetary disks.