Stress clamp experiments on multicellular tumor spheroids

The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate. We observe that a stress of 10 kPa is sufficient to drastically reduce growth by inhibition of cell proliferation mainly in the core of the spheroid. We compare the results to a simple numerical model developed to describe the role of mechanics in cancer progression.     

High average power spectral beam combining of four fiber amplifiers to 8.2 kW

We report on the incoherent beam combination of the four narrow-linewidth fiber amplifier chains running at different wavelengths. Each main amplifier stage consists of a large-mode-area photonic crystal fiber delivering more than 2 kW of optical power. The four output beams are spectrally combined to a single beam with an output power of 8.2 kW using a polarization-independent dielectric reflective diffraction grating mainly preserving the beam quality of the individual fiber amplifiers.     

88 W 0.5 mJ femtosecond laser pulses from two coherently combined fiber amplifiers

The generation of 0.5 mJ femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of 175 kHz producing 88 W of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach-Zehnder interferometer, which has been stabilized with a H?nsch-Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as λ/70 rad at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.     

135 W average-power femtosecond pulses at 520 nm from a frequency-doubled fiber laser system

We present a high-average-power femtosecond laser system at 520 nm central wavelength. The laser system delivers sub-500 fs pulses with 135 W average power at a pulse repetition rate of 5.25 MHz. Excellent beam quality is provided by high power fiber amplifiers and maintained during frequency doubling, resulting in a beam quality factor of M2<1.2. To our knowledge, the system presented here is the highest average power green laser source generating femtosecond pulses with diffraction-limited beam quality.     

Pump-enhanced optical parametric oscillator generating continuous wave tunable terahertz radiation

We demonstrate a tunable cw terahertz (THz) parametric oscillator based on periodically poled MgO-doped lithium niobate, directly converting the 1030 nm pump wave into the THz regime. The tunability ranges from 1.2 to 2.9 THz at output power levels between 0.3 and 3.9 μW. To overcome the high pump threshold caused by THz absorption in the nonlinear crystal, we employ an enhancement cavity with a finesse of 500 at the pump wavelength. The intracavity pump threshold at 1.4 THz is measured to be 350 W for a crystal length of 2.5 cm.     

Influence of flexible spacers on liquid-crystalline self-assembly of T-shaped bolaamphiphiles

T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col(hex)/p6mm, Col(rec)/p2gg, Col(squ)/p4gm and Col(squ)/p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col(rec)/c2mm phase made up of rhombic cylinders with the Col(squ)/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col(rec)/p2gg to Col(squ)/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.     

Enhanced stability of a protein with increasing temperature

The unusual stability of a structured but locally flexible protein, human growth hormone (hGH) at pH 2.7, was investigated using the temperature dependence of the nanosecond-picosecond dynamics of the backbone amide groups obtained from (15)N NMR relaxation data. It is found that the flexibility of the backbone of the helices decreases with temperature in the range from 24 °C to ～40 °C, corresponding to an increasing stability. A concomitant increase with temperature of the electrostatic interactions between charged residues forming an interhelical network of salt bridges at the center of the four-helix core suggests that these interactions give rise to the decreasing flexibility and increasing stability of the protein. However, numerous hydrophobic interactions in the interior of the four-helix core may also contribute. Above ～40 °C, where the thermal energy overcomes the electrostatic and hydrophobic interactions, a substantial increase in the flexibility of the helix backbones results in a highly positive contribution from the local conformational heat capacity, C(p,?conf), of the helix backbones to the total heat capacity, C(p), of the protein. This reduces the change in heat capacity upon unfolding, ΔC(p), increases the change in the Gibbs free energy, ΔG(unfold), and stabilizes the protein at high temperatures. A similar decrease in flexibility is found near other salt bridges in hGH and in Calmodulin and may be of general importance for the thermostability of proteins and, in particular, of the salt bridge intensive thermophilic proteins.     

Site‐Selective Late‐Stage Aromatic [18F]Fluorination via Aryl Sulfonium Salts

Site‐selective functionalization of C?H bonds in small complex molecules is a long‐standing challenge in organic chemistry. Herein, we report a broadly applicable and site‐selective aromatic C?H dibenzothiophenylation reaction. The conceptual advantage of this transformation is further demonstrated through the two‐step C?H [¹⁸F]fluorination of a series of marketed small‐molecule drugs.     

Wetting Phenomena and their Effect on the Electrochemical Performance of Surface‐Tailored Lithium Metal Electrodes in Contact with Cross‐linked Polymeric Electrolytes

Li metal batteries (LMBs) containing cross‐linked polymer electrolytes (PEs) are auspicious candidates for next‐generation batteries. However, the wetting behavior of PEs on uneven Li metal surfaces has been neglected in most studies. Herein, it is shown that microscale defect sites with curved edges play an important role in a wettability‐dependent electrodeposition. The wettability and the viscoelastic properties of PEs are correlated, and the impact of wettability on the nucleation and diffusion near the Li|PE interface is distinguished. It is found that the curvature of the edges is a key factor for the investigation of wetting phenomena. The appearance of microscale defects and phase separation are identified as main causes for erratic nucleation. It is emphasized that the implementation of stable and consistent long‐term cycling performance of LMBs using PEs requires a deeper understanding of the “soft‐solid”–solid contact between PEs and inherently rough Li metal surfaces.