Transient Lifetime Research Articles

Influence of conduction heterogeneities on transient spatiotemporal chaos in cardiac excitable media

Life-threatening cardiac arrhythmias such as ventricular fibrillation are often based on chaotic spiral or scroll wave dynamics which can be self-terminating. In this work, we investigate the influence of conduction heterogeneities on the duration of such chaotic transients in generic models of excitable cardiac media. We observe that low and medium densities of heterogeneities extend the average transient lifetime, while at high densities very long transients, potentially persistent chaos, and periodic attractors occur. Published by the American Physical Society 2024

Slow Conformational Exchange between Partially Folded and Near-Native States of Ubiquitin: Evidence for a Multistate Folding Model.

The mechanism by which small proteins fold, i.e., via intermediates or via a two-state mechanism, is a subject of intense investigation. Intermediate states in the folding pathways of these proteins are sparsely populated due to transient lifetimes under normal conditions rendering them transparent to a majority of the biophysical methods employed for structural, thermodynamic, and kinetic characterization, which attributes are essential for understanding the cooperative folding/unfolding of such proteins. Dynamic NMR spectroscopy has enabled the characterization of folding intermediates of ubiquitin that exist in equilibrium under conditions of low pH and denaturants. At low pH, an unlocked state defined as N' is in fast exchange with an invisible state, U″, as observed by CEST NMR. Addition of urea to ubiquitin at pH 2 creates two new states F' and U', which are in slow exchange (kF'→U' = 0.14 and kU'→F' = 0.28 s-1) as indicated by longitudinal ZZ-magnetization exchange spectroscopy. High-resolution solution NMR structures of F' show it to be in an "unlocked" conformation with measurable changes in rotational diffusion, translational diffusion, and rotational correlational times. U' is characterized by the presence of just the highly conserved N-terminal β1-β2 hairpin. The folding of ubiquitin is cooperative and is nucleated by the formation of an N-terminal β-hairpin followed by significant hydrophobic collapse of the protein core resulting in the formation of bulk of the secondary structural elements stabilized by extensive tertiary contacts. U' and F' may thus be described as early and late folding intermediates in the ubiquitin folding pathway.

Underwater Acoustic Camouflage by Wettability Transition on Laser Textured Superhydrophobic Metasurfaces

AbstractThe superhydrophobicity of submerged surfaces typically pertains to the trapped air film at the liquid–solid interface, subject to wettability transitions from a Cassie–Baxter state to more unstable states that gradually collapse to high retention regimes, which are energetically more favorable. In this work, the dynamic evolution of those transient metastable states is correlated to the underwater acoustic performance of laser textured superhydrophobic surfaces, resolving the dependence of the ultrasound spectral response with the immersion time to capture the genuine contribution of the hierarchical subwavelength morphology, regardless of the air layer effects. Acoustic wave attenuation of the incident ultrasound energy is extensively quantified in transmission, accounting for instantaneous broadband sound blocking (>30 dB) within the spectral range 0.5–1.5 MHz. As a result of the air layer detachment with the immersion time, transmission coefficients increase accordingly, while acoustic fields in reflection unexpectedly evolve toward stealthiness and naïve acoustic camouflage, mostly ascribable to dissipative mechanisms at air layer interfaces. The intrinsic decay of the air layer effect is tentatively determined at different frequencies, since quantitative understanding of the transient lifetime governing underwater surface wettability is critical to design stable superhydrophobic character of laser induced subwavelength metastructures on the most promising acoustic materials – from eco‐friendly natural to artificial.

Perovskite Quantum Dots Lasing in Double-Heterostructure through Energy Transfer.

Planar double heterostructures were initially investigated and have been successfully applied in III-V semiconductor lasers due to their excellent roles in confining both the photons and carriers. Here, we design and fabricate a (PEA)2Csn-1PbnX3n+1 (quasi-2D)/CsPbBr3 QD/quasi-2D double-heterostructure sandwiched in a 3/2 λ DBR microcavity, and then demonstrate a single-mode pure-green lasing with a threshold of 53.7 μJ/cm2 under nanosecond-pulsed optical pumping. The thresholds of these heterostructure devices decrease statistically by about 50% compared to the control group with no energy donor layers, PMMA/QD/PMMA in an identical microcavity. We show that there is efficient energy transfer from the barrier regions of the quasi-2D phases to the QD layer by transient absorption and luminescence lifetime spectra and that such energy transfer leads to marked threshold reduction. This work indicates that the double-heterostructure configurations should play a significant role in the future perovskite electrically pumped laser.

Efficient separation of photo-generated carriers for in-situ induction of PDI cation radicals to enhance the photocatalytic performance of PDI supramolecules

In order to investigate whether the formation of hydrogen bonds can affect the degradation products of pollutants, a photocatalyst PDI-SE was obtained by end substituting perylene tetracarboxylic dianhydride with serine (SE) in this paper. As a reference, PDI-IS with isopropylamine (IS) terminal alkyl substitution was synthesized simultaneously. Their photocatalytic performance to decompose phenol and tetrabromobisphenol A (TBBPA) were investigated. PDI-SE could degrade 79.3% of phenol or 68.4% of TBBPA within 4 h under visible light. The degradation products of TBBPA were tracked using high-resolution mass spectrometry. The morphology, composition, structure, and optoelectronic properties of two photocatalysts, particularly their transient absorption spectra and fluorescence lifetime were studied. We also conducted theoretical calculations on their binding energy with phenol or TBBPA, distribution and separation of electron and hole of excited state PDI-SE and PDI-IS supramolecules. Due to the formation of hydrogen bonds the binding energy of PDI-SE with phenol or TBBPA is 1.24 eV or 1.99 eV, which is stronger than that of PDI-IS (0.85 eV or 1.66 eV). Although both PDI-SE and PDI-IS can form free radical cations in excited states, the high separation of electrons and holes of PDI-SE leads to a longer lifetime of free radical cations, so caused its excellent photocatalytic activity compared to PDI-IS. This article proposes a new strategy based on molecular design to promote efficient separation of photogenerated electrons and holes, thereby forming stronger oxidizing PDI cationic radicals in situ to enhance the photocatalytic performance of PDI supramolecules.

Photosensitizers Based on Bichromophoric Dyads Combining Ru(II)-Polypyridyl Complexes and Dissymmetric Perylene Monoimide Derivatives: The Nontrivial Role of Ligand Substitution.

The covalent modification of Ru(II) polypyridyl complexes (RPCs) with organic chromophores is a powerful strategy to obtain metal-based photosensitizer agents (PSs) with improved performance for application in photodynamic therapy (PDT). In this respect, perylene-imides are of particular interest due to their rich chemical-physical repertoire, and it is therefore quite surprising that their combination with RPCs has been poorly considered so far. Herein, we report on the photophysical behavior of two newly synthesized RPCs bearing a perylene monoimide appendant (PMI-Ad). Differently from the majority of RPCs-perylene-imides dyads, these chromophores are dissymmetric and are tethered to the metal centers through a single C-C bond in the 3- or 5-position of 1,10-phenanthroline (Ru-3PMI-Ad and Ru-5PMI-Ad). Both compounds show excellent singlet oxygen photosensitizing activity, with quantum yields reaching >90% in the case of Ru-3PMI-Ad. A combined spectroscopic and theoretical analysis, also involving transient absorption and luminescence lifetime measurements, demonstrates that both compounds undergo intersystem crossing on a very fast time scale (tens of picoseconds) and with high efficiency. Our results further demonstrate that the increased electron delocalization between the metal center and the PMI-Ad chromophore observed for Ru-3PMI-Ad additionally contributes to increase the singlet oxygen quantum yields by prolonging the lifetime of the triplet state.

Targeted nonviral delivery of genome editors in vivo

Cell-type-specific in vivo delivery of genome editing molecules is the next breakthrough that will drive biological discovery and transform the field of cell and gene therapy. Here, we discuss recent advances in the delivery of CRISPR-Cas genome editors either as preassembled ribonucleoproteins or encoded in mRNA. Both strategies avoid pitfalls of viral vector-mediated delivery and offer advantages including transient editor lifetime and potentially streamlined manufacturing capability that are already proving valuable for clinical use. We review current applications and future opportunities of these emerging delivery approaches that could make genome editing more efficacious and accessible in the future.

Recombination and Trapping of Excess Carriers in n-InSb

The effect of trapping on the transient and steady-state lifetimes of excess carriers is investigated in InSb of n-type conductivity. Photoconductive decay and direct current measurements are used to characterize the starting material and infrared photodiodes. The large difference between the transient and steady-state lifetimes is explained by the trapping of minority carriers at the acceptor centers within the two-level recombination model. The recombination parameters of the traps are estimated.

Can apparently transient life events trigger long-term lower urinary tract symptoms?

One-time life events such as neurological injury can result in lifelong lower urinary tract symptoms (LUTS). However, it is unclear whether an apparently transient life event can also trigger long-term LUTS. This review examines the possibility of an association and hypothesizes the pathogenesis. A pubmed search was conducted using the MeSH words "life change events," "child abuse," or "stress disorders, Posttraumatic", and LUTS. Additional manuscripts were identified by a hand and citation search. Long-term LUTS was noted following temporally remote childhood sexual abuse, adverse childhood experiences, and stressful experiences in adults. There was evidence for an association of childhood sexual abuse and adverse childhood events with both storage as well as voiding LUTS. There was limited evidence that the number of adverse childhood events might increase the risk and severity of LUTS. There was evidence of an association between post-traumatic stress disorder in adults and LUTS. The finding of mental health disorders in such patients could explain some but not all of the observed association suggesting that other factors might also be important. There is an association noted between apparently transient lifetime events and the subsequent reporting of LUTS. The timing of these adverse experiences might be important in determining the propensity for clinical manifestation. There is a need to explore this association, establish causality, and determine the underlying etiopathogenesis.

Controlling carbodiimide-driven reaction networks through the reversible formation of pyridine adducts.

Carbodiimides and pyridines form reversible adducts that slowly deliver carbodiimide "fuels" to out-of-equilibrium reaction networks, slowing activation kinetics and elongating transient state lifetimes. More-nucleophilic pyridines give more adduct under typical conditions. This approach can be used to extend the lifetimes of transient polymer hydrogels.

The controllable growth of CsPb2Cl5 nanosheets and their application as a stable photodetector for ultraviolet

CsPb2Cl5 nanosheets were grown on different substrates by a simple solution method using dilute hydrochloric acid and absolute ethanol as solvents. The effect of temperature on the nanosheet growth was investigated. It was turned out that lower temperature is beneficial to the formation of nucleation of nanosheets. The nanosheet size changed from 20 μm to 60 μm, and the thickness gradually decreased from 750 nm to 120 nm as the growth temperature increased. The nucleation rate and distribution caused by contact angle induced solute transport on different substrates were obtained. The CsPb2Cl5 nanosheets were confirmed to possess a large Stokes shift and broad emission spectrum in the PL and prolonged carrier lifetime in transient fluorescence lifetime measurements. An ultraviolet photodetector based on CsPb2Cl5 nanosheets was reported for the first time. An extremely low dark current (pA-level), large on–off ratio and a fast response time with a rise time of 17 ms and a decay time of 32 ms were obtained. The detector placed in air without any package for over 2100 h still maintains 85 % photocurrent of the initial value.

Short-lived chimera states.

In the classic Kuramoto system of coupled two-dimensional rotators, chimera states characterized by the coexistence of synchronous and asynchronous groups of oscillators are long-lived because the average lifetime of these states increases exponentially with the system size. Recently, it was discovered that, when the rotators in the Kuramoto model are three-dimensional, the chimera states become short-lived in the sense that their lifetime scales with only the logarithm of the dimension-augmenting perturbation. We introduce transverse-stability analysis to understand the short-lived chimera states. In particular, on the unit sphere representing three-dimensional (3D) rotations, the long-lived chimera states in the classic Kuramoto system occur on the equator, to which latitudinal perturbations that make the rotations 3D are transverse. We demonstrate that the largest transverse Lyapunov exponent calculated with respect to these long-lived chimera states is typically positive, making them short-lived. The transverse-stability analysis turns the previous numerical scaling law of the transient lifetime into an exact formula: the "free" proportional constant in the original scaling law can now be precisely determined in terms of the largest transverse Lyapunov exponent. Our analysis reinforces the speculation that in physical systems, chimera states can be short-lived as they are vulnerable to any perturbations that have a component transverse to the invariant subspace in which they live.

Solid-state fluorophores featuring a combined hybridized local and charge transfer excited state and aggregation-induced emission as efficient emitters for electroluminescent devices

Solid-state fluorophores with high fluorescence efficiency and charge transportation have always been of great interest as emitters for organic light-emitting diodes (OLEDs). Mostly, donor (D)-acceptor (A) molecules holding prominent intramolecular charge transfer exhibit low fluorescence quantum yield. Here, we report a series of D–A–D type hybridized local and charge transfer (HLCT) excited state fluorophores (TBz, T2FBz, TFBz, TBBz, TPyBz, and TNz) containing benzo[c][1,2,5]thiadiazole (Bz) and its derivatives (5,6-difluoro-2,1,3-benzo[c][1,2,5]thiadiazole (2FBz), 5–2,1,3-benzo[c][1,2,5]thiadiazole (FBz), naphtho[1,2-c:5,6-c']bis([1,2,5]thiadiazole) (BBz), [1,2,5]thiadiazolo[3,4-c]pyridine (PyBz), and naphtho[2,3-c][1,2,5]thiadiazole (Nz)) as acceptor cores end-capped with tetraphenylethylene (TPE) as a donor and aggregation-induced emission (AIE)-luminogen. The different variations in the molecular structures of the cores render compounds with wide-ranging electronic and photophysical properties. The HLCT and AIE properties of these compounds are confirmed by theoretical calculations, solvatochromic behaviors, and transient decay lifetimes analyses. They show intense fluorescence emissions with good thermal stability and hole mobility, leading to effective utilization as emitters in OLEDs. The resulting devices demonstrate strong green to orange-red electroluminescent (EL) emissions with decent EL performance (Lmax of 6030–20220 cd m−1, CEmax of 6.26–13.18 cd A−1, and EQEmax of 3.51–5.11%). Among them, OLED fabricated with TBBz realized the best EL performance (Lmax of 11115 cd m−2, CEmax of, 12.03 cd A−1, EQEmax of 5.11%) with orange emission (λEL = 592 nm, CIE coordinates (0.53, 0.46)).

11.2: The Effect of Doping Distribution on the Property of Green Phosphorescent Organic Light‐Emitting Diodes

In mass production OLED structures, doping ratio distribution across the thickness of emitting layer is not uniform owing to the linear evaporating configuration, where dopant and host materials are added in different sources. In this study, we firstly confirmed that different types of doping distribution among emitting layer of green phosphorescent OLED exhibited over 15% difference of current efficiency. By carefully designing and comparing emitting layers with a series of doping distribution modes, we found that dramatic variation of doping ratio near electron blocking layer was the critical factor. Then, trapping behavior of dopant molecules was confirmed to affect the carrier distribution among the emitting layer according to analysis of current density‐voltage (JV) and capacitance‐voltage (CV) curves from carrier only devices based on two types of doping distribution modes. Combining with the result of hole‐electron recombination zone (RZ), the area where possessed both high doping ratio and excitons recombination probability exhibited a high current efficiency and low driving voltage. Finally, PL and EL transient decay lifetime combined with triplet‐polaron quenching (TPQ) efficiency measurement demonstrated that TPQ was the main factor causing current efficiency difference between two types of doping distribution modes. Therefore, the doping distribution and trapping property of dopant material in emission layer should be carefully evaluated for OLED devices for mass production.

High-resolution spectroscopy of Holmium Perchlorate: Establishment of wavelength standard for spectrophotometer

We have investigated the excited state dynamics of Holmium Oxide (Ho2O3) dissolved in perchloric acid using ultrafast optical pump-probe spectroscopy by exciting the samples with laser light at 350 nm and 550 nm and detecting in the visible region. Using an ultrafast spectroscopic approach, the stability of Ho2O3 solution has been examined. UV–Visible spectroscopy revealed 14 bands in the Ho2O3 absorption spectrum and by using ultrafast transient absorption spectroscopy, we have probed the dynamics of the excited state and studied transient absorption lifetime in the visible range. We obtained multi-exponential dynamics of carrier relaxation for Ho2O3, with time constants spanning from 0.07 to >500 ps. The lifetime of molecules has been shown to be on the order of picoseconds (ps), proving the stability of Ho2O3 solution and making it suitable for use as a wavelength standard for spectrophotometer calibration.

Chemically Fueled Dissipative Cross-Linking of Protein Hydrogels Mediated by Protein Unfolding.

Cells assemble dynamic protein-based nanostructures far from equilibrium, such as microtubules, in a process referred to as dissipative assembly. Synthetic analogues have utilized chemical fuels and reaction networks to form transient hydrogels and molecular assemblies from small molecule or synthetic polymer building blocks. Here, we demonstrate dissipative cross-linking of transient protein hydrogels using a redox cycle, which exhibit protein unfolding-dependent lifetimes and mechanical properties. Fast oxidation of cysteine groups on bovine serum albumin by hydrogen peroxide, the chemical fuel, formed transient hydrogels with disulfide bond cross-links that degraded over hours by a slow reductive back reaction. Interestingly, despite increased cross-linking, the hydrogel lifetime decreased as a function of increasing denaturant concentration. Experiments showed that the solvent-accessible cysteine concentration increased with increasing denaturant concentration due to unfolding of secondary structures. The increased cysteine concentration consumed more fuel, which led to less direction oxidation of the reducing agent and affected a shorter hydrogel lifetime. Increased hydrogel stiffness, disulfide cross-linking density, and decreased oxidation of redox-sensitive fluorescent probes at a high denaturant concentration provided evidence supporting the unveiling of additional cysteine cross-linking sites and more rapid consumption of hydrogen peroxide at higher denaturant concentrations. Taken together, the results indicate that the protein secondary structure mediated the transient hydrogel lifetime and mechanical properties by mediating the redox reactions, a feature unique to biomacromolecules that exhibit a higher order structure. While prior works have focused on the effects of the fuel concentration on dissipative assembly of non-biological molecules, this work demonstrates that the protein structure, even in nearly fully denatured proteins, can exert similar control over reaction kinetics, lifetime, and resulting mechanical properties of transient hydrogels.

Soluble Diphenylhexatriene Dimers for Intramolecular Singlet Fission with High Triplet Energy.

Intramolecular singlet fission (iSF) facilitates single-molecule exciton multiplication, converting an excited singlet state to a pair of triplet states within a single molecule. A critical parameter in determining the feasibility of SF-enhanced photovoltaic designs is the triplet energy; many existing iSF materials have triplet energies too low for efficient transfer to silicon via a photon multiplier scheme. In this work, a series of six novel dimers based upon the high-triplet-energy, SF-active chromophore, 1,6-diphenyl-1,3,5-hexatriene (DPH) [E(T1) ∼ 1.5 eV], were designed, synthesized, and characterized. Transient absorption spectroscopy and fluorescence lifetime studies reveal that five of the dimers display iSF activity, with time constants for singlet fission varying between 7 ± 2 ps and 2.2 ± 0.2 ns and a high triplet yield of 163 ± 63% in the best-performing dimer. A strong dependence of the rate of fission on the coupling geometry is demonstrated. For optimized iSF behavior, close spatial proximity and minimal through-bond communication are found to be crucial for balancing the rate of SF against the reverse recombination process.

Study on ZnO quantum dot ligands for inkjet printing of light-emitting diodes

Inkjet printing as a contact-free, high material utilization, low cost, patternable solution processing technology, may become the future color quantum-dot light-emitting diodes (QLED) production of the key technology. However, owing to the existence of the pixel structure of the substrate array, the film prepared by inkjet printing technology is not so smooth and uniform as that by spin coating technology, which affects the luminescence performance of the device. Therefore, it is necessary to study the film forming mechanism and process of inkjet printing. In order to solve the above problems, this paper focuses on the material and process problems of preparing high-quality electronic transport layer ZnO thin films by inkjet printing. From the perspective of ligand, the ZnO quantum dot material, which is an indispensable electron transport layer, is optimized to prepare the thin films with good morphology and stability in air, and the methods to improve the performances of inkjet printing QLED devices are explored. Firstly, the drying process and influence mechanism of ZnO quantum dot ink in air are investigated. As the thickness of ZnO quantum dot film prepared by inkjet printing increases, the film becomes loose and the surface becomes rough with the continuous extension of the time in the air. These changes make the efficiency of the QLED device decrease and the luminous region uneven. The reason for this phenomenon is that after the ZnO quantum dots are printed into the pixel pit, the random Brownian motion of quantum dots will continue in the process of solvent evaporation. In this process, the ligand ethanolamine connected to the surface of ZnO quantum dots will fall off with the movement and cannot play the role in dispersing the quantum dots. Besides, the external water oxygen and carbon dioxide attach to the film. The combination between the two effects makes the ZnO quantum dots aggregate into large particles and the film becomes loose and porous. In this paper, we use ethylenediamine tetraacetic acid (EDTA) as ligand to synthesize ZnO quantum dots, which can effectively improve this phenomenon. The carboxyl group at the end of EDTA is more stable in connection with ZnO quantum dots. Moreover, the EDTA has multiple branch chains, which makes it have steric hindrance effect and can disperse ZnO effectively. A smooth and compact film with a roughness of 1.97 nm is prepared by inkjet printing. After 40 min exposure to air, the film is still able to maintain a stable morphology. Then, based on the EDTA-ZnO quantum dots synthesized above, red QLED devices with optimized performance are prepared. The current efficiency of the spin-coating device is 16.8 cd/A, which is better than that of the ZnO quantum dots before modification. The EDTA ligand passivates the surface defects of ZnO, alleviates the quenching phenomenon when contacting red quantum dots, and improves the fluorescence quantum efficiency and transient fluorescence lifetime of quantum dots on the electron transport layer. In addition, the EDTA regulates the carrier transport performance, making the carrier recombination of the device more balanced. In the inkjet printing device, the improvement of device morphology plays a leading role in improving the performance. The inkjet printing QLED based on EDTA-ZnO achieves a current efficiency of 9.24 cd/A, and maintains a current efficiency of 6.82 cd/A after 40 min in air, which are 23% and 89% higher than those of the control device. This work provides a reference for solving the problems of film thickness increase and morphology variation caused by particle agglomeration in the preparation of large area devices in inkjet printing.

InSb фотодіоди (огляд. Частина V)

The results of research on the recombination of non-equilibrium charge carriers in n-InSb single crystals are analyzed. It is shown that the Shockley-Reed-Hall recombination models described in the literature are unable to explain the experimental results obtained in single crystals of applied quality, which are used to create infrared photodiodes. The proposed model of recombination with the participation of two independent levels, one of which is an acceptor. The model is based on the results of experimental studies of the lifetime in n-type InSb obtained from measurements of photoconductivity relaxation under pulsed laser excitation in the temperature range of 77-250 K. For the measurements, n-type conductivity single crystals grown by Czochralski method and obtained from several sources were used. The concentration of charge carriers in the samples at a temperature of 77 K varied within 1014-1016 cm-3. The kinetics of photoconductivity was studied in n-InSb samples before and after the formation of diffused p+-n junctions. The diffusion temperature of the cadmium acceptor impurity varied between 380 and 420 0С. It is shown that in the samples after the formation of the p-n junction, the lifetime can be limited by the effect of the trapping of minority carriers to the acceptor level, which is located at a distance of 60 meV from the bottom of the conduction band. The model allows describing the dependence of lifetime on temperature and carrier concentration in the doping range of 1014 - 1016 cm-3. From the comparison of stationary and transient lifetime, conclusions are drawn regarding the existence of the effect of the trapping of minority carriers in the material of n-type conductivity, which is responsible for the excess tunnel current in photodiodes, generation-recombination and low-frequency 1/f noise. It is assumed that acceptor traps can be caused by the generation of dislocations during the formation of a diffused junction.

Electronic Properties of Light- and Elevated Temperature-Induced Degradation in Float-Zone Silicon

Light- and elevated temperature-induced degradation (LeTID) causes long-term instabilities, especially in passivated emitter and rear cells, leading to severe performance loss of commercial modules. Despite the hundreds of LeTID reports available in the literature, there is little consensus regarding the underlying defects and defect formation mechanism responsible for this degradation and its exact electronic properties. Recently, it has been shown that a form of carrier-induced degradation similar to that of LeTID is also observed in some high-purity silicon crystals grown by the float-zone method. In this work, using deep level transient spectroscopy and lifetime spectroscopy, we study the role of nitrogen on the degradation. Intentional contaminated samples with different and known level of nitrogen have been specially grown and characterized for this study. We detect the appearance of a set of majority carrier traps in the degraded state of the samples with activation energies 0.1 (H85), 0.43 (H270A), 0.39 (H270B), and 0.46 eV (H200) with respect to the valence band, from which H270A appears to correlate with the degradation. The results show that the extent of degradation in the nitrogen-rich samples is at least double that of the nitrogen-lean samples.