Low-energy Amplitudes Research Articles

CTNI-27. SYSTEMIC DELIVERY OF LOW ENERGY RADIOFREQUENCY ELECTROMAGNETIC FIELDS FOR THE TREATMENT OF PATIENTS WITH PRIMARY BRAIN TUMORS

Abstract BACKGROUND Tumor Treating Fields plus maintenance temozolomide (mTMZ) showed a survival advantage in the first-line glioblastoma (GBM) treatment. The survival benefit remains limited in patients with unmethylated MGMT gene promoter. The AutEMsys device emits low-energy amplitude modulated systemic electromagnetic fields (EMF) at patient specific frequencies. It is an outpatient procedure that can be integrated with mTMZ. METHODS This study involved a prospective compassionate access program targeting adult GBM patients using an intrabuccal EMF exposure via AutEMsys in addition to chemoRT+mTMZ. The program explored the effects on survival and patients’ reported quality-of-life (QOL) by EORTC-QL-C30. Patients underwent a 90-minute session of EMF exposure therapy repeated every 2 weeks until progression, deterioration in QOL or death. All patients had pathological specimens for diagnosis, IDH mutation status through NGS techniques, and MGMT promoter region methylation status. RESULTS 31 participants were enrolled, including 29 with GBM and 2 with diffuse midline glioma. 14 patients (45%) received EMF+chemoRT followed by EMF+mTMZ and 17 patients (55%) received EMF+mTMZ (post chemoRT). Survival time was measured from the start of mTMZ to the date of the last follow-up. The median overall survival (mOS) for all 31 patients was 26.0 months (95% CI: 14.4 – 37.2 months). Specifically for 21 patients with unmethylated MGMT, the mOS was 25.0 months (95% CI: 15.9 – 34.1 months). Similarly, for the 28 patients with IDH wildtype status, the mOS remained 26.0 months (95% CI: 9.6 – 42.4 months). The addition of AutEMsys with chemoRT+mTMZ demonstrated an improved role functioning in 79% of patients with 25% of these with >10-point score. CONCLUSION The AutEMsys device has shown promising initial results when added to chemoRT+mTMZ treatment of GBM. These findings warrant further prospective investigation and validation in a multicenter clinical trial setting.

Nonrelativistic effective field theory with a resonance field

We discuss shallow resonances in the nonrelativistic scattering of two particles using an effective field theory (EFT) that includes an auxiliary field with the quantum numbers of the resonance. We construct the manifestly renormalized scattering amplitude up to next-to-leading order in a systematic expansion. For a narrow resonance, the amplitude is perturbative except in the immediate vicinity of the resonance poles. It naturally has a zero in the low-energy region, analogous to the Ramsauer-Townsend effect. For a broad resonance, the leading-order amplitude is nonperturbative almost everywhere in the regime of validity of the EFT. We regain the results of an EFT without the auxiliary field, which is equivalent to the effective-range expansion with large scattering length and effective range. We also consider an additional fine tuning leading to a low-energy amplitude zero even for a broad resonance. We show that in all cases the requirement of renormalizability when the auxiliary field is not a ghost ensures the resonance poles are in the lower half of the complex momentum plane, as expected by other arguments. The systematic character of the EFT expansion is exemplified with a toy model serving as underlying theory.

Sum rules in the standard model effective field theory from helicity amplitudes

The dispersion relation of an elastic 4-point amplitude in the forward direction leads to a sum rule that connects the low energy amplitude to the high energy observables. We perform a classification of these sum rules based on massless helicity amplitudes. With this classification, we are able to systematically write down the sum rules for the dimension-6 operators of the Standard Model Effective Field Theory (SMEFT), some of which are absent in previous literatures. These sum rules offer distinct insights on the relations between the operator coefficients in the EFT and the properties of the full theory that generates them. Their applicability goes beyond tree level, and in some cases can be used as a practical method of computing the one loop contributions to low energy observables. They also provide an interesting perspective for understanding the custodial symmetries of the SM Higgs and fermion sectors.

Low energy amplitude modulated radiofrequency electromagnetic fields in combination with standard treatment or as monotherapy to show improvement in quality of life in patients with advanced hepatocellular carcinoma.

290 Background: Hepatocellular carcinoma (HCC) is a fatal cancer without curative option for most patients. Hence the importance to improve health related quality of life (HRQoL). Amplitude-modulated radiofrequency electromagnetic fields (EMF), as a novel and non-toxic therapy, has potential for improving HRQoL in advanced HCC patients. Methods: An open-label, single center, prospective clinical protocol was performed in advanced HCC patients as an initial and salvage treatment modality. Systemic exposure to EMF was used in combination with a systemic conventional treatment or as a single treatment. A spoon-shaped antenna placed in the oral cavity delivered EMF over 90 minutes with monthly repetitions until death or consent withdrawal. The effect on HRQoL was the primary objective of this study. Patients answered the EORTC-C30 v3.0 questionnaires prior to every EMF exposure. Clinically meaningful change (CMC) and time to deterioration (TTD) for Global Health (QoL), Role Functioning (RF) and Physical Functioning (PF) were used in the analysis. Results: From March 2018 to April 2020, 55 advanced HCC patients were submitted to 373 EMF exposures. 41/55 (75%) patients had repetitive exposures (mean # 4, ranging from 2-16). 87% were male, median age was 67, 84% were BLCL-C, 16% were Child-Pugh B, 29% had extra-hepatic metastasis, 55% had failed previous treatment and 71% had documented radiological progression. 31(56%) patients received EMF in combination with systemic therapy (28 TKI and 3 anti-PDL1). 24 patients received EMF as a single treatment modality. The mean baseline score was 68.1 for QoL and 77.1 for RF and PF. 61%, 76% and 49% of patients experienced positive change in QoL, RF and PS scores immediately prior to the second exposure, respectively. +CMC was reported in 20%, 17% and 32% of patients, respectively for QoL, RF and PS. The median QoL TTD was not reached. The median RF TTD was 7.2 month and the median PF TTD was 11.9 month. The median RF TTD for patients in combination treatment was 11.4 months and in a single treatment was 13.5 month. The median PF TTD for patients in combination treatment was 12.8 months and in single treatment was 14.5 month. Conclusions: Advanced HCC patients showed positive changes in QoL, RF and PF HRQoL scores after single exposure to EMF. The benefit from EMF in HRQoL was durable both in combination with TKI or as a single modality in advanced HCC patients. These results support future development as a novel palliative treatment modality in advanced HCC patients. Clinical trial information: NCT 01686412.

Low energy amplitude modulated radiofrequency electromagnetic fields to show antitumor effect in combination with standard treatment or as monotherapy in patients with advanced hepatocellular carcinoma.

332 Background: Exposure to amplitude-modulated radiofrequency electromagnetic fields (EMF) in immortalized hepatocellular carcinoma (HCC) cell cultures and xenograft models demonstrated anti-tumor effect. Patients with advanced HCC exposed to systemic EMF showed objective response with potential survival benefit. Methods: An open-label, single center, prospective clinical protocol was performed in advanced HCC patients as an initial, second or third treatment modality. Systemic exposure to EMF modulated at patient-specific frequencies was applied as an add-on strategy (combination) to systemic conventional treatment or as a single therapeutic modality. A spoon-shaped antenna placed in the oral cavity delivered EMF over 90 minutes with monthly repetitions until death or consent of withdrawal. The primary objective was overall survival (OS) in comparison with historical control group of 45 advanced patients HCC from the same institution. Retrospective radiological review was conducted by two independent radiologists for objective response (OR) using RECIST1.1 criterion. Results: From March 2018 to April 2020, 55 advanced HCC patients were submitted to 373 EMF exposures. 87% were male, median age of 67, 84% were BLCL-C, 16% were Child-Pugh B, 29% had extra-hepatic metastasis, 55% had failed previous treatment and 71% had documented radiological progression. 31(56%) patients received EMF in combination with systemic therapy (25 sorafenib, 3 lenvatinib, 3 nivolumab). 24 patients received EMF as single treatment modality. The median OS for the entire patient cohort was 11.5 months. The median OS for combination treatment was 12.0 month and the median OS for single modality was 11.3 months. The median OS for the historical control was 5.3 month. The median OS from the entire cohort and the historical control were significant different (p = 0.0026) but the median OS from combination and single modality were not (p = 0.3434). Radiological images were available from 38(69%) patients. There were 6/38 (16%) documented objective responses (1 CR and 5 PR) and 30/38 (79%) patients experienced disease control. 4/21 (19%) OR were in patients using TKIs + EMF and 2/17 (12%) OR were in patients using EMF alone. Conclusions: EMF showed objective anti-tumor effect in combination with TKI or as single modality in advanced HCC patients. EMF showed improvement in overall survival in comparison with the historical control group supporting future development as a novel systemic treatment modality in advanced HCC patients. Clinical trial information: NCT 01686412.

Effects of the dynamic cathode sheath on electron transport at the initial period of HiPIMS pulse studied by Langmuir probe measurements and 2D PIC-MCC simulation

In high power impulse magnetron sputtering (HiPIMS) discharge, the cathode sheath is a particularly vital section which determines the spatial distribution of electric field and the energy and transport of charged particles. In this work, a single Langmuir probe is employed to explore the effects of dynamic cathode sheath on electron transport at the initial period of HiPIMS pulse. Measurements show that the electron temperature is as high as ~20 eV and the plasma density is much lower than ~1015–1016 m−3 at the beginning of HiPIMS pulse t < 3 μs; correspondingly, a feature of small low-energy amplitude and extended high-energy tail is found in the electron energy distribution function (EEDF). And the high-energy electrons can escape the magnetic trap and gradually diffuse to further axial positions, even to z = 140 mm with only several microseconds delay. The diffusion coefficient of electrons D⊥ is larger than the typical Bohm diffusion at z > 32 mm in our discharge case. The two-dimension Particle-in-cell Monte Carlo collision (2D PIC-MCC) simulation results are well in agreement with the experimental results. The net positive charge density ∆n near the target is lower than ~+9.2×1014 m−3 at t = 0.5 μs, and the charge separation is up to ~0.4. In this case, the cathode sheath has a large thickness and the axial electric field EZ outside the sheath is as strong as dozens of 10 kVm−1. The simulation results confirm, for the case of the expanding sheath, (i) the electrons can be accelerated and escape the magnetic trap with weak constraint; (ii) the electron group can maintain their kinetic energy when they diffuse from the ionization region (IR) to bulk plasma (BP). When the net charge density increases to ~+3×1016 m−3 at t = 2.5 μs, the sheath thickness is condensed to ~1 mm with ~600 V voltage drop.

A Study on the Correlation Between Poles and Cuts in ππ Scattering**Supported by National Natural Science Foundation of China uder Grant Nos. 11805059, 11805012, 11805037, and Fundamental Research Funds for the Central Universities, the Joint Large Scale Scientific Facility Funds of the NSFC and Chinese Academy of Sciences (CAS) under Grant No. U1832121, Shanghai Pujiang Program under Grant No. 18PJ1401000,

In this paper we propose a dispersive method to describe two-body scattering with unitarity imposed. This approach is applied to elastic ππ scattering. The amplitudes keep single-channel unitarity and describe the experimental data well, and the low-energy amplitudes are consistent with that of chiral perturbation theory. The pole locations of the σ, f0(980), ρ(770) and f2(1270) and their couplings to ππ are obtained. A virtual state appearing in the isospin-two S-wave is confirmed. The correlations between the left (and right) hand cut and the poles are discussed. Our results show that the poles are more sensitive to the right hand cut rather than the left hand cut. The proposed method could be used to study other two-body scattering processes.

1604P - Exposure to low energy amplitude modulated radiofrequency electromagnetic fields (EMF) is associated with rapid improvement in quality of life (QoL) status in patients with advanced hepatocellular carcinoma (HCC), using various analyses of EORTC-C30

BackgroundPatient-centered endpoints, overall survival (OS) and QoL (where the benefit is detectable by the patient as an improvement in symptoms or functional capacity), are considered valid “direct” endpoints by the FDA. While EORTC-C30 is an accepted indicator of QoL, there is no accepted standard for time to QoL status improvement, nor any accepted standard of analysis for EORTC-C30 data. MethodsA single-group, open-label, feasibility study was performed to assess QoL status in HCC patients exposed to modulated EMF at patient-specific frequencies. A 120-min outpatient EMF exposure procedure was performed every 30 days until significant QoL deterioration or death. An oral spoon-shaped RF antenna applicator was used to apply EMF while individuals were kept in supine position. EORTC-C30 v3.0 questionnaires were answered by individuals immediately prior to every EMF exposure. The 17 QoL parameters were divided into those measuring improvement (G+ functional scales and global health status/QOL) and those measuring deterioration (G- symptom scales). QoL index was calculated as (mean G+) – (mean G-). Different QoL index calculations were made using three groups of QoL parameters: all 17 QoL parameters, 15 QoL parameters (removing Functional scales and Symptom scales) and 3 QoL parameters (restricted to Functional scales, Symptom scales and Global health status/QOL). A change of +/-5% in QoL index was considered a clinically relevant improvement/deterioration in QoL status. Results42 HCC were exposed to 151 EMF procedures. 4,530 QoL data points were collected for analysis, with 0.1% missing data. QoL index was measured at baseline and 30 days after the baseline exposure procedure. Using the 3 QoL index calculation methods (17 QoL, 15 QoL and 3 QoL) measured 30 days from the baseline exposure, QoL status improved in 63%, 59% and 74% of HCC patients respectively. ConclusionsRapid and significant improvement in QoL status in HCC patients exposed to EMF was detected within 30 days of exposure regardless of the QoL index calculation methods used. Clinical trial identificationNCT 01686412. Editorial acknowledgementLuiz Fernando Reis PhD, Research Director Hospital Sírio Libanês, São Paulo, Brazil, Riad Younes MD and Bertram Wiedenmann PhD MD. Legal entity responsible for the studyHospital Sírio Libanês. FundingHas not received any funding. DisclosureF.P. Costa: Leadership role: Autem Medical. A. Iemma: Honoraria (institution): Autem Medical. F. Soares: Honoraria (institution): Autem Medical. J. Tuszynski: Advisory / Consultancy: Autem Medical. All other authors have declared no conflicts of interest.

Softness and amplitudes\u2019 positivity for spinning particles

We derive positivity bounds for scattering amplitudes of particles with arbitrary spin using unitarity, analyticity and crossing symmetry. The bounds imply the positivity of certain low-energy coefficients of the effective action that controls the dynamics of the light degrees of freedom. We show that low-energy amplitudes strictly softer than O(p4) do not admit unitary ultraviolet completions unless the theory is free. This enforces a bound on the energy growth of scattering amplitudes in the region of validity of the effective theory. We discuss explicit examples including the Goldstino from spontaneous supersymmetry breaking, and the theory of a spin-1/2 fermion with a shift symmetry.

Time optimal control of the monodomain model in cardiac electrophysiology

An optimal control approach to a simplified reaction–diffusion system describing cardiac defibrillation is proposed that allows for joint optimization of shape and duration of defibrillation pulses. Within the framework, optimized multi-phasic pulses with low energy, short duration and/or low amplitude can be designed according to specific needs. The approach is based on a novel time optimal control formulation for the monodomain model, which takes into consideration the dynamical system properties of the uncontrolled equation. The highly complex dynamics requires a consistent discretization of first- and second-order information to guarantee effective optimization schemes leading to successful defibrillation. Numerical examples underline the efficiency of the proposed method.

Faddeev calculations of theK¯NNsystem with a chirally motivatedK¯Ninteraction. I. Low-energyK−dscattering and antikaonic deuterium

A chirally-motivated coupled-channel $\bar{K}N$ potential, reproducing all low-energy experimental data on $K^- p$ scattering and kaonic hydrogen and suitable for using in accurate few-body calculations, was constructed. The potential was used for calculations of low-energy amplitudes of the elastic $K^- d$ scattering using Faddeev-type AGS equations with coupled $\bar{K}NN$ and $\pi \Sigma N$ channels. A complex $K^- - d$ potential reproducing the three-body $K^- d$ amplitudes was constructed and used for calculation of $1s$ level shift and width of kaonic deuterium. The predicted shift $\Delta E_{1s}^{K^- d} \sim -830$ eV and width $\Gamma_{1s}^{K^- d} \sim 1055$ eV are close to our previous results obtained with phenomenological $\bar{K}N$ potentials.

INFRARED FIXED POINT IN THE STRONG RUNNING COUPLING: UNRAVELING THE ΔI = 1/2 PUZZLE IN K-DECAYS

In this paper, we present an explanation for the ΔI = 1/2 rule in K-decays based on the premise of an infrared fixed point α IR in the running coupling αs of quantum chromodynamics (QCD) for three light quarks u, d, s. At the fixed point, the quark condensate [Formula: see text] spontaneously breaks scale and chiral SU (3)L× SU (3)R symmetry. Consequently, the low-lying spectrum contains nine Nambu–Goldstone bosons: π, K, η and a QCD dilaton σ. We identify σ as the f0(500) resonance and construct a chiral-scale perturbation theory χPTσ for low-energy amplitudes expanded in αs about α IR . The ΔI = 1/2 rule emerges in the leading order of χPTσ through a σ-pole term KS→σ→ππ, with a gKSσ coupling fixed by data on γγ→π0π0 and KS→γγ. We also determine R IR ≈5 for the nonperturbative Drell–Yan ratio at α IR .

Effects of Electronic Mixing in Ruthenium(II) Complexes with Two Equivalent Acceptor Ligands. Spectroscopic, Electrochemical, and Computational Studies

The lowest energy metal to ligand charge transfer (MLCT) absorption bands found in ambient solutions of [Ru(NH(3))(4)(Y-py)(2)](2+) and [Ru(L)(2)(bpy)(2)](+) complexes (Y-py a pyridine ligand and (L)(n) a substituted acetonylacetonate, halide, am(m)ine, etc.) consist of two partly resolved absorption envelopes, MLCT(lo) and MLCT(hi). The lower energy absorption envelope, MLCT(lo), in these spectra has the larger amplitude for the bis-(Y-py) complexes, but the smaller amplitude for the bis-bpy the complexes. Time-dependent density functional theory (TD-DFT) approaches have been used to model 14 bis-bpy, three bis-(Y-py), and three mono-bpy complexes. The modeling indicates that the lowest unoccupied molecular orbital (LUMO) of each bis-(Y-py) complex corresponds to the antisymmetric combination of individual Y-py acceptor orbitals and that the transition involving the highest occupied molecular orbital (HOMO) and LUMO (HOMO-->LUMO) is the dominant contribution to MLCT(lo) in this class of complexes. The LUMO of each bis-bpy complex that contains a C(2) symmetry axis also corresponds largely to the antisymmetric combination of individual ligand acceptor orbitals, while the LUMOs are more complex when there is no C(2) axis; furthermore, the energy difference between the HOMO-->LUMO and HOMO-->LUMO+1 transitions is too small (<1000 cm(-1)) to resolve in the spectra of the bis-bpy complexes in ambient solutions. Relatively weak MLCT(lo) absorption contributions are found for all of the [Ru(L)(2)(bpy)(2)](m+) complexes examined, but they are experimentally best defined in the spectra of the (L)(2) = X-acac complexes. TD-DFT modeling of the HOMO-->LUMO transition of [Ru(L)(4)bpy](m+) complexes indicates that it is too weak to be detected and occurs at significantly lower energy (about 3000-5000 cm(-1)) than the observed MLCT absorptions. Since the chemical properties of MLCT excited states are generally correlated with the HOMO and/or LUMO properties of the complexes, such very weak HOMO-->LUMO transitions can complicate the use of spectroscopic information in their assessment. As an example, it is observed that the correlation lines between the absorption energy maxima and the differences in ground state oxidation and reduction potentials (DeltaE(1/2)) have much smaller slopes for the bis-bpy than the mono-bpy complexes. However, the observed MLCT(lo) and the calculated HOMO-->LUMO transitions of bis-bpy complexes correlate very similarly with DeltaE(1/2) and this indicates that it is the low energy and small amplitude component of the lowest energy MLCT absorption band that is most appropriately correlated with excited state chemistry, not the absorption maximum as is often assumed.

Aspects of the [formula omitted] SYM amplitude – Wilson polygon duality

We discuss formulation of Wilson polygon – MHV amplitude duality at the perturbative level in various regularizations. For four gluons it is shown that at one loop one can formulate diagrammatic correspondence interpolating between the dimensional regularization and the off-shell one. We suggest new interpretation of all types of box diagrams in terms of the dual simplex in dimensional regularization and describe its degeneration to the Wilson polygon. The interesting nullification phenomena for the low-energy amplitudes in the Higgsed phase has been found.

Collisional phenomena involving rydberg atoms

The theory of collisions of Rydberg atoms with rare-gas atoms at thermal energies is reviewed. A central feature of the analysis is that the interaction of a highly excited atom with a perturber may be viewed as the scattering of the active electron from the perturber. Therefore, the low-energy electron-scattering amplitude plays a crucial role in the formulation of the problem. In the field-free regime, the transitions considered are between different angular momentum states belonging to the same principal quantum number n. The generalization of the theory to the case of a weak, static electric field is also presented. In this case, the appropriate initial and final states arc Stark states. The transition from zero field to weak field is discussed, and numerical results are presented that illustrate several important effects.

Novel sets of coupling expansion parameters for low-energy pQCD

In quantum theory, physical amplitudes are usually presented in the form of Feynman perturbation series in powers of coupling constant $\al .$ However, it is known that these amplitudes are not regular functions at $\alpha=0 .$ For QCD, we propose new sets of expansion parameters ${\bf w}_k(\as)$ that reflect singularity at $\as=0 $ and should be used instead of powers $\as^k.$ Their explicit form is motivated by the so called Analytic Perturbation Theory. These parameters reveal saturation in a strong coupling case at the level $\as^{eff}(\as\gg1)={\bf w}_1(\as\gg 1) \sim 0.5 .$ They can be used for quanitative analysis of divers low-energy amplitudes. We argue that this new picture with non-power sets of perturbation expansion parameters, as well as the saturation feature, is of a rather general nature.

Some remarks on the Padé unitarization of low-energy amplitudes

We present a critical analysis of Padé-based methods for the unitarization of low energy amplitudes. We show that the use of certain Padé approximants to describe the resonance region may lead to inaccurate determinations. In particular, we find that in the (weakly coupled) Linear Sigma Model the unitarization of the low energy amplitude through the inverse amplitude method does not recover the correct values for the mass and width of the sigma. Alternative sequences of Padés are studied and we find that the diagonal sequences (i.e., [N/N]) have much better convergence properties.

Nucleon decay in gauge unified models with intersectingD6-branes

Baryon number violation is discussed in gauge unified orbifold models of type II string theory with intersecting Dirichlet branes. We consider setups of $D6$-branes which extend along the flat Minkowski space-time directions and wrap around three cycles of the internal 6D manifold. Our study is motivated by the enhancement effect of low energy amplitudes anticipated for M theory and type II string theory models with matter modes localized at points of the internal manifold. The conformal field theory formalism is used to evaluate the open string amplitudes at tree level. We study the single baryon number violating processes of dimension 6 and 5, involving four quarks and leptons and in supersymmetry models, two pairs of matter fermions and superpartner sfermions. The higher order processes associated with the baryon number violating operators of dimension 7 and 9 are also examined, but in a qualitative way. We discuss the low energy representation of string theory amplitudes in terms of infinite series of poles associated to exchange of string Regge resonance and compactification modes. The comparison of string amplitudes with the equivalent field theory amplitudes is first studied in the large compactification radius limit. Proceeding next to the finite compactification radius case, we present a numerical study of the ratio of string to field theory amplitudes based on semirealistic gauge unified nonsupersymmetric and supersymmetric models employing the ${Z}_{3}$ and ${Z}_{2}\ifmmode\times\else\texttimes\fi{}{Z}_{2}$ orbifolds. We find a moderate enhancement of string amplitudes which becomes manifest in the regime where the gauge symmetry breaking mass parameter exceeds the compactification mass parameter, corresponding to a gauge unification in a seven dimensional space-time.

Unraveling the f0 nature by connecting KLOE and BABAR data through analyticity

We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes like: φ→e + e - M and φ→γM, starting from cross-section data on e + e -→φM, where M is a generic light scalar or pseudoscalar meson. In particular this procedure is constructed to obtain predictions on the radiative decay rate which are crucially linked on the assumed quark structure for the meson M under consideration. Three cases are analyzed: M = η, M = f 0(q¯) and M = f 0(qq¯). While in the η case the estimate of the branching fraction for the radiative decay φ→ηγ is in agreement with the data, in the case of f 0, such agreement is obtained only under the hypothesis of a tetraquark scalar meson.

Remarks on Limits on String Scale from Proton Decay and Low-Energy amplitudes in Braneworld scenario

We discuss IR limit of four-fermion scattering amplitudes in braneworld models including intersecting-branes and SUSY SU(5) GUT version of it. With certain compactification where instanton effect is negligible, grand unification condition in D6-D6 intersecting-branes scenario subject to experimental constraint on proton decay provides possibility for upper limit on the string scale, $M_S$, through relationship between the string coupling, $g_s$, and the string scale. We discuss how IR divergence is related to number of twisted fields we have to introduce into intersection region and how it can change IR behaviour of tree-level amplitudes in various intersecting-branes models. Using number of twisted fields, we identify some intersecting-branes models whose tree-level amplitudes are purely stringy in nature and automatically proportional to $g_s/M^2_{S}$ at low energy. They are consequently suppressed by the string scale. For comparison, we also derive limit on the lower bound of the string scale from experimental constraint on proton decay induced from purely stringy contribution in the coincident-branes model, the limit is about $10^5$ TeV.